61689121 Automotive Engine Electronics

114
Automotive ICS DR. b b How to dLgnose and . repair the automotive Compufer Control System. .-rp'& - .t

Transcript of 61689121 Automotive Engine Electronics

Page 1: 61689121 Automotive Engine Electronics

A u t o m o t i v e

I C S

DR.

b b How to dLgnose and

. repair the automotive Compufer Control System. .-rp'& -

.t

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Automotive Engine Electronics

How to Diagnose and Repair the Automotive Computer Control System

by Dr. Robert C. McElroy

Second Revised Edition

Accuracy Publishing, Homestead, Florida

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photo by Rick Bernskoetter

Bob McElroy at the wheel of his Hilborn Fuel Injected Corvette at an SCCA autocross. Note video camera attached to windshield.

Published by: Accuracy Publishing Co. Post Office Box 514 Homestead, FL 33035-051 4

Corvette Cover Artwork Compliments of: Micrografx Corporation

I 1511

Bob McElroy

All rights reserved. No part of this book may be used or re- produced or transmitted in any form or by any means, electronic or mechanical, including photocopying, record- ing or by any information storage and retrieval system without prior written permission from the author except in the case of brief quotations embodied in critical reviews and articles.

Copyright 1987,1988 by Robert C. McElroy, Ph.D. First Printing 1987 Second Printing 1988, revised Third Printing 1988, revised Printed in the United States of America

Library of Congress Cataloging in Publication Data McElroy, Robert C.

Automotive Engine Electronics Understand, Diagnose & Repair: Fuel, Ignition

& Computer Control Systems 1. Automotive Electronics--Computers, sensors, etc. 2. Electricity and Electronics--Computers, sensors, etc 3. Diagnosis--Computers, sensors, etc. 4. Mathematics--Computers, sensors, etc I. Title ISBN 0-929603-37-0 Sof tcover

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SECTION I -- Sensors & Systems SECTION II -- Driveability Diagnosis

TOPIC PAGE

Table of Contents 3 Objective 4 Foreward 5 Introduction 6 About the Author 8 Background of Today's Automobile 9 Electrical & Electronic Terms 11 OHM'S Law 16 Series Circuits 18 Parallel Circuits 20 Series Parallel Circuits 2 1 Diodes 22 Despikeing and Clamping Diodes 24 Transistors 25 Point Style Ignition Systems 26 HE1 -- High Energy Ignition 29 EST -- Electronic Spark Timing 3 1 Distributorless Ignition Systems -- CI 33 CCC -- Computer Command Control 35 EFI -- Electronic Fuel Injection 38 PFI -- Port Fuel Injection 40 Transition -- fuel to electronic systems 43 Throttle Position Sensor -- TPS 44 Temperature Sensors -- CTS & MAT 46 Manifold Absolute Pressure -- MAP 47 Electronic Spark Control -- ESC 48 Mass Air Flow Sensor -- MAF 49 Eshaust Gas Recirculation -- EGR 50 Idle Air Control -- IAC 53 Vehicle Speed Sensor -- VSS 54 Evaporative Emission Control -- EEC 55

TOPIC PAGE

Driveability Diagnosis Philosophy Systems Approach to Diagnosis Electronic Control Module -- ECM ALCL Terminal Circuits Scanner Use Integrator & Block Learn Scanner Error Diagnostic Procedures Digital Multimeter -- DMM Jumper Wires & Connectors Computer Harness Adaptive Tester Diagnostics & ECM Voltage Checks Continuity Tests CHAT Basic Test Procedures CHAT Advanced Testing Procedures Advanced Circuit Testing ECM Codes Open & Closed Loop Fuel Injector Balance Test

SECTION Ill --

SELECTED ECM VOLTAGES &WIRE DIAGRAMS Which can be read with CHAT.

Note: CHAT will interface BCM and GMP4 design ECMs. BCM and GMP4 circuits have not been included in this publication. CCC and EFI systems incorporating "edgeboard" connectors were not included.

CHAT is covered by U.S. Patent No. 4,690,475 and is available from Diagnostic Products Co. P.O. Box 1136, Homestead, Fl. 33090

Diagnostic Products Co. is the Electronics Subsidiary of Spectra Investments Ltd. Inc.

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Objectives of this manual:

1. Provide a comprehensive general explanation for electronically spark controlled and fuel injected engines manufactured by GM.

2. Provide specific information for the use of ALCL "scan" tools.

3. Provide specific information for the use of "CHAT' the Computer Harness Adaptive Tester.

4. Provide specific information for the use of CHAT to perform voltage and continuity testing for all wires and circuits interfacing the ECM.

This manual has been prepared for:

1. Professional Technicians in the field of automotive repair.

2. Students of Automotive Technology.

3. Automotive Enthusiasts who wish to know more about contemporary automotive engine electronics.

This manual has been prepared with a "systems" approach:

1. Diagnosis and repair must be performed in a step by step method, to ensure that you "isolate" the problem, and not simply replace what seems to be wrong.

2. Automotive systems are broken down so that you can see how they are intended to work in a conceptual method. When you understand the general concept you will be able to apply your understanding to systems and components which differ from those included in this manual.

This manual is not intended to replace applicable service manuals pertaining to the service of any automobile. This manual is intended to complement service manuals specifically prepared by the vehicle manufacturer.

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In order to understand the complex na- ture of today's automobile we must be able to speak and understand the lan- guage used to describe these vehicles. You may be reluctant to want to learn anything, but you have made it this far by purchasing this book. A book which you can use and learn new technology from. A book written to help you each and every day on the job.

Actually, when you start to dig into this material it will be fun and interesting. The trick is to just take your time and master these basic terms and concepts. One thing that you really need to do is understand how these things work, at least on a simple level. This book will approach everything on a simple level and use this basic principle of under- standing to build upon.

Some of the things which we will look at in the beginning will seem too simple to really work with. However, I have seen too many repairs done incorrectly. When you really analyze what you are doing the bottom line really must be to get the car fixed. Hopefully, this will happen the first time or else you will have a recheck to perform. Rechecks mean that you will not be making money on the next car waiting for you. Therefore, the fewer rechecks the more money you ought to make. That seems simple enough, doesn't it?

Always try and do the job right the first time even if it takes a few extra minutes. One good example would be a water pump. If it leaks then you will probably have to do the whole job over and I don't know of anyone who wants to redo a water pump. The same sort of thinking applies to this new technology. If the car still has a driveability problem then it is going to be a comeback and rechecks eat your earnings.

NO RECHECKS

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This book has been prepared with the objective of presenting basic concepts which apply to the modern automobile which uses a small computer or ECM to control fuel delivery to the engine. In order to understand how this system functions, you will be presented the basic concepts relating to how air and fuel management is accomplished.

If you know and understand the relation- ships between the sensor inputs and computer outputs you will be able to diagnose problems which occur with the modern automobile. No one book can be expected to provide all information which can apply to all situations. How- ever, the information provided will be of value when you must diagnose and re- pair these vehicles.

As you gain experience with computer equipped cars and trucks you will find that they do perform and react in a predictable way. There are certain things which you must know and under- stand. Some things must work or the vehicle simply will not run. These facts will be covered so that you will be able to quickly and accurately determine if these necessary inputs are present. Use of a definite strategy will mean that your diagnosis is done quickly and in a logical procedure.

Your use of a definite method of analysis will increase your productivity and reduce the number of comebacks and your number of rechecks. This increase in productivity will make you a better tech- nician which should also correspond to an increase in your paycheck.

In order that you understand how this system works we will first investigate the ignition system. Understanding of today's ignition systems is 100% essential. Proper fuel delivery to the engine is based upon this input signal and without it the vehicle will not run due to loss of both spark and fuel delivery.

NO WRENCHES ON

THE RED TERMINAL

Always remove the ground cable first. If you accidentally hit some sheet metal you will not risk blowing up the battery.

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I believe that many technicians do not have a good understanding of how igni- tion systems operate. Therefore, we will study a conventional point-type ignition first. If you know and understand how this system works you will not have any difficulty with electronic systems. More cars are being designed each year without distributors. As you progress through your study of this book, you will clearly come to understand why a distributor is not needed. As you learn how these systems operate and how other inputs can provide the same necessary signal you will be able to figure out and trou- bleshoot systems which you have not per- sonally worked on yet.

As you study this manual and compare its information to the cars which you work with daily you will become a better tech- nician. Additional education at your local technical school or community col- lege will also help you to be more profes- sional in your duties. If you are not already certified by ASE, you are encour- aged to participate. ASE certification is a highly desirable goal and those techni- cians who wear the ASE patch take pride in their accomplishment. You make your living as a technician. Vehicles which you work on daily are highly complex and the more you know about these vehicles the better off you are. Your need for techni- cal literature and education have never been greater. You demonstrate your professionalism when you wear the ASE certification patch.

YOUR TECHNICAL J O B

THE MORE YOU KNOW

THE MORE THINGS

YOU CAN FIX

FASTER &

MORE RELIABLE

EVERYONE BENEFITS FROM TECHNICIAN

CERTIFICATION

SUPPORT IT!

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I walked into my local Chevrolet dealer and asked for a job as a junior mechanic and grease monkey during my summer break from college in 1969. That did not last long; soon I was tearing apart engines and trying to figure out how to get them running again. The more things which I could fix, the more work I got in the shop.

I drove my first race car in 1965. It was while I was a senior in high school in State College, Pennsylvania. We even raced in the winter. I remember trying to run over a snowbank during one event while rac- ing on the icy surface. This interest in racing has probably been the key to why I have always kept a strong interest in automotives.

Over the years I have raced many differ- ent types ofvehicles including the likes of jeep, ferrari, pantera, vega, corvair, mus- tang, police cars, and my favorite, the corvette. Those police cars came from when I taught High Performance Driving to police officers at the Texas Transpor- tation Institute.

I have always felt that if you are going to win on the track then you must field the best car. Even if you happen to be the best driver around, if your machine is not set up properly then you cannot win. I have never gone to an event with the idea to lose. Of course I don't always win and I do get beat sometimes, but I don't lose. It really is a state of mind where you feel confident about your ability and your

equipment. When you know what you are supposed to do, and you do it well, then you can really enjoy what and how you do things. I would hope that you personally feel that way about your occupation ... if you do not then I hope that this book will help you to gain this type of confidence.

For a period of three years I was in the position of resident engine instructor, at one of the 31 GM training centers in operation at that time, after having been recruited by General Motors in 1983 . In Detroit we would be given product infor- mation which would be used to conduct classes about new engine systems and their operation for dealership techni- cians who would attend our classes. All this new information was great, but this information had to be passed on to the fellows and an occasional lady who actu- ally "turns a wrench" to make a living. It really was a lot of fun.

Additional qualifications to be your au- thor to write this book besides my expe- rience with GM, racing, and having been a "Chevrolet Certified Technician" would include formal college education background of a BS, MA, and finally a Ph.D. in industrial education from Texas A&M University. In 1987 I was one of 375 people inducted into the Automo- bile Hall of Fame in Midland, Michigan as an "ASIA/ASE 'World Class' Techni- cian" for holding all 16 ASE area certifi- cations.

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Way back in the old days, pre-computer cars that is, we basically concerned our- selves with three types of problems: 1) fuel, 2) ignition, or 3) mechanical. How- ever, today there is an additional 4) elec- tronic problem area which really gives technicians a tough time. This latest addition to our problems is the most dif- ficult to understand. You simply cannot take apart a transistor with a 9/16" or lOmm wrench. Since you cannot easily disassemble this electronic stuff it means that you will probably have to learn about these things either on your own or in a class somewhere. This book will help you understand how automotive electronics work and this book will help you fix today's electronically complex cars.

When cars were simple it was not too difficult to figure out which area theprob- lem was in and then it could be attacked. If there was a question about ignition, then did spark come out of the plug wire? If not then points were pretty easy to fix. I remember a 1970 LT-1 corvette at the dealership, the ticket said "won't run". I found the car, it would crank but not start. I popped off a plug wire and hung it on top of the air cleaner wingnut; crank engine again and no spark but the 12 volt test light says power to the coil and a good

ground. Hmmm ... the points must be locked up. Off with the chrome shroud, remember this is a corvette, off with the distributor cap ... what the .... So much for my first introduction to transistorized ignition.

Today's cars may affect you the same way. There is no denying that cars are much more complex than ever before and there is no alternative to under- standing how they operate. Because of Federal regulations for improved fuel and emission characteristics of our ve- hicles it became necessary to develop more sophisticated engine control sys- tems to meet these new standards. Many of you reading this book look favorably on the past but you know that "simple" cars are no longer built; also you know that the carburetor is in fact only a "cali- brated leak" which will not do the job today.

Microprocessors are the heart of the computer or Electronic Control Mod- ule, ECM for short. Microprocessors get information from many sensors placed all over the vehicle. Microprocessors take this information and run it through the operational program recorded per- manently inside the machine found on

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10 ROMS and PROMS. After all this analy- sis is done then some sort of output will come from the ECM such as when to inject fuel and how long the injectors are to be held open.

This entire information transmission process at first seems almost impossible to figure out. However, this is not the case. There are some very logical rela- tionships which do exist and you as a professional technician already know the basic principles of engine operation. We will take these things which you are al- ready familiar with and use them as the basis for all the new systems. New sys- tems may be new but they accomplish the same sort of things as the old systems. Whether or not new systems are better is something which most mechanics and technicians have personal opinions about ...j ust ask one! Let's face it, there is no alternative ...y ou have to know how the new systems operate if we are going to be successful in this occupation.

How did you learn to be a technician in the first place? Were you taught by other mechanics or did you attend a technical training program? I expect that you actu- ally have some of both. You have already invested heavily in your education; some people would call this the "School of Hard Knocks." You have invested thou- sands of dollars in your tool box. Every time the tool truck comes by you can think of additional tools which will make you more productive. Tools are an in- vestment in your future, there is no other alternative there.

When you finish reading this book you will find it to be an excellent reference. Others will want to use this book. As with any tool you will need to have it available at times. You know who borrows your tools and this book is no exception. A saying that I have seen on one master technician's toolbox is "I would rather loan you my dog than my tools. The dog always comes home." It applies to this book too.

IF YOU WANT TO FIRE TWO SPARK PLUGS AT THE SAME

TIME, HERE IS HOW IT'S DONE.

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First off let's look at wire. With wire we can "pipe" electricity to every device in the car which needs energy to operate. Most wires in the car are made from copper. Some wires in the body harness of the car are aluminum but these are rare, and require special wire repair tech- niques.

Copper is a very good conductor. A conductor is a material which allows elec- trons to flow through it easily. If you are going to keep the electrons in the wire you must cover the wire with a tough material which will not let the electrons get out of the wire. This material is called an insulator. Most wires are covered with an insulator, which is generally a type of plastic.

Enough electrons moving will create an electrical current. How many electrons you need to perform a job depends on the load. A crank or starting motor requires

INSULATION

Wires carry electrons. Electrical pressure is called voltage. Quantity of electrons is

measured in amps.

a large electric cable cLming right-from the battery, while a dome light needs only a small wire to work effectively. I The electrical pressure to both the crank motor and dome light are the same. Electrical Pressure is called VOLTAGE. Both items get the same voltage or pres- sure coming from the battery because

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12 wires conduct the electrons to each item. If the battery has a 12 volt potential difference between the B + (red) and B- (black) terminals at the battery and we connect a wire to the B + and a wire to the B- and then go to the end of each wire and place a voltmeter between them we should have 12 volts shown on the meter.

If both the crank motor and the dome light get the same electrical pressure then why the different size of electrical wires and cables? Both devices get 12 volts. The difference is how much work each device must do. That large cable to the crank motor will allow many more elec- trons to move than the small wire to the dome light. The quantity or amount of electrons flowing is called AMPS.

BAl lERY VOLTAGE (PRESSURE) IS CARRIED BY WIRES

- CRANK - SY M BOL - MOTOR I -

DOME LIGHT AND CRANK MOTOR GET 12 VOLTS

CRANK MOTOR USES MORE AMPS THAN DOME LIGHT CRANK MOTOR USES LARGE CABLE

DOME LIGHT USES A WIRE

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INSUlATION

WIRE A LARGE WIRE WILL CARRY MQRE AMPS

REMEMBER -- TjYE SAME V ' L TAG€ IS AFTLIED TO B U M WRES!

If I had two cars, one with a 4 cylinder engine breathing through a lbbl carbure- tor and the other car had tunnel ram and two Holley Double Pumpers ... then which one will use the most fuel? The tunnel ram will use the most fuel because it needs that fuel to do its job properly, just like the crank motor will need a lot of amps to do its job properly. If both our cars use the same type of pump gas, then in order to make more horsepower we must deliver more fuel to the engine. Therefore we invest in the big 110 gallon per hour electric fuel pump and use a I/ 2" or larger fuel line between the fuel tank and tunnel ram.

If a fuel fitting leaks our car will not run the way it is supposed to. If an electrical wire starts to corrode it will not conduct current properly. If a fuel line breaks the car will not run. If an electrical wire is cut the component will not work. If gasoline spills and is ignited your car may be destroyed. If an electrical wire is shorted to ground the electrical system and pos- sibly the car might burn up.

SHORT CIRCUIT

BRACKET HAS WORN THROUGH THE INSULATION ON THIS WIRE CAUSING A SHORT TO GROUND

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Current, when flowing inside a good wire, can be considered to have no resistance to its flow. Wires act as a pipeline of energy to the item or component we need to run. When current cannot flow easily to a component, resistance has been added to our circuit.

Resistance in a wire is bad. It generates heat inside the wire and it means that not enough current will get to the component on the end of the wire. The component may not work properly because it does not have enough current to perform within its operating limits. This reduc- tion in current may cause the component to fail.

Resistance in a component means that the item will perform work for us. Imag- ine you are holding a fire hose with water spraying into the air. If you aimed this hose at the side of a mountain you would start to wash away the mountain and the stream of water would be doing work for you. The mountain becomes resistance to the flow of water. Work is performed as you wash away the mountain.

Each electrical item which performs work in the car has some resistance. Resistance means that current cannot simply flow right through the item to ground. The current must do something which we want it to do in order for the current to get to ground. This internal electrical activity or flow will operate each electrical component in the car for US.

DO NOT USE CRIMP CONNECTORS ON TODAY'S CAR.

CRIMP CONNECTORS PROMOTE CORROSION WHICH CREATES RESISTANCE AND HEAT IN THE WIRE.

Crimp connectors used for repair on this late model T Bird will create electrical problems for the rest of this car's life.

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Some components offer static resistance to current flow and some items have dynamic resistance to current flow. If you have ever taken apart a solenoid coil you have found that there are many feet of wire in the coil. The length of wire and the size of wire cause resistance inside the coil. This is an example of a static resis- tance.

Light bulbs and crank motors have dy- namic resistance to the flow of current. When these items are working current cannot get across them fast enough. As the armature moves past the brushes in the crank motor, current flow is not con- tinuous because current is directed to different parts of the armature winding because of the contact point placement under the brush. A crank motor which is locked up can have a very high current draw.

MAGNETIC FIELD

CRANK MOTOR

COMMUTATOR

MAGNETIC FIELD

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A mathematical relationship exists be- tween volts, amps and ohms in any elec- trical circuit. George Simon Ohm discov- ered the relationship between these fac- tors and named the formula after him- self, hence the name Ohm's Law.

Mr. Ohm found that volts or pressure in a circuit will move a quantity of electrons or amps through a defined resistance or ohms. This relationship means that if you know any two of the three factors then it is possible to determine the third item mathematically.

Although many technicians have diffi- culty in learning Ohm's Law it is a very important relationship which definitely needs to be mastered. Specifically, when you know and can even visualize (yes actually see in your mind) how these three aspects of electrical flow work to- gether then you will be in a much better position to fin the modern car which uses a microcomputer to control engine op- eration.

The Electronic Control Module or ECM does everything electrically. Voltage is the language of the ECM. Voltage is pressure. The ECM will control electri- cal pressure to get things done. Just like you flip a switch to turn the lights on, the computer will controlvoltage to a transis- tor (functioning as an electrical switch) in

Ohm's Law Terms: E = Voltage I = Amps R = Resistance

Ohm's Law:

T E --

I - R

E = I X R

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order to activate an output. For example, the air conditioning compressor clutch which would be disabled during wide open throttle to allow maximum accel- eration.

Ohm's Law will help you fix problem cars. The ECM is designed to handle only 1/2 amp on most circuits. This means that the relays and solenoids must have 20 ohm or greater resistance or you will blow the ECM. Only "protected" circuits can handle currents greater than 1/2 amp, an example being the fuel injector solenoid but this circuit is only pulsed in millisec- onds (thousands of a second).

RESISTANCE SYMBOL

OMEGA SIGN IS USED TO SHOW OHMS

OHMS

In Ohm's Law: Amps x Ohms Volts

12VOLT

12 A M P 1 OHM

12VOLT

1 A M P 12 OHM

12VOLT

A M P 24 OHM

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In a series circuit all the components or devices are hooked up end-to-end. This arrangement means that all the current (amps) in the circuit is the same through

BLOWER MOTOR RESISTOR BLOCK SERIES CIRCUIT DIAGRAM

each componenet used in the circuit.

Current flow in a series circuit is like a water hose. All the water passes through the hose from end to end. In a series circuit the same amount of current passes through each component.

SERIES CIRCUIT LAWS:

1. In a series circuit the current flowing in the circuit is the same at all points in the circuit.

2. Total resistance of the series circuit is the total of all individual resistances present in the the circuit.

3. The sum of all voltage drops, across each resistance, in a series circuit equals the applied or source voltage.

MOTOR w

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Question: In a series circuit with three resistors, calculate the total resistance (R T), and calculate the current flow using Ohm's Law.

12 VOLT wd Step 1 -- list given values I H I

Step 2 -- determine total resistance R T

R T = R 1 + R 2 + R 3 R T = 2 Q + 4 n + 6 Q = 1 2 n

R 3 AAAII

I

Step 3 -- apply Ohm's Law to E 12 V I = - = - = l a m p determine amp flow R 12 fl

Question -- Now that you know the amount of current flowing calculate the voltage drop across each resistor using Ohm's Law.

E = I X R Ohms' Law equation

to determine voltaqe drop across each resistor multiply amp flow times individual resistor values

E r l = 1 ~ ~ 1 = I ampx2R = 2wI ts Er2 = I X R ~ = 1 ampx4R = 4volts Er3 = IxR3 = 1 ampx6R = 6volts total voltage drop = Erl + Et2 + Er3 = 2 + 4 + 6 = 12 volts .

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A parallel circuit has two or more branches in which all the positive termi- nals are connected to a common point and all the negative terminals connected to a common point. Therefore, the same voltage is applied across each compo- nent.

Parallel Circuit Laws :

1. In a parallel circuit, the voltage is the same across each branch.

2. Total current in the circuit is the sum of the current flow in each branch.

3. Total resistance of the parallel cir- cuit is always less than the smallest resistive branch.

Maximum Panel Brightness

Set rheostat for O ohm. 12 u. is applied across each bulb.

E Ohm's Law equation I = w I = elr I = 12vl2Oohm 1 .6 amp {per bulb)

Amps total = amps per bulb x number of bulbs lt=.6ax5=3amp

INSTRUMENT PANEL LIGHTING PARALLEL CIRCUIT DIAGRAM

RHEOSTAT I

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Series - parallel circuits combine aspects of both series and parallel circuits. In the series part of the circuit all the current passes through one circuit component. In the parallel circuit there are multiple paths for the current to pass through.

In this example the rheostat is the series load and the bulbs are the parallel load.

To calculate current (amps) first deter- mine the resistance of the parallel com- ponents. Add the parallel resistance to the series resistance in order to deter- mine total resistance. Use Ohm's Law in order to determine amp flow in this cir- cuit.

Voltage drop across series and parallel segments can be determined by Ohm's Law by multiplying amps times resis- tance for the series segment.

Parallel resistance = 20 ohm / 5 = 4 ohm Series resistance = 8 ohm Total resistance = 4 + 8 = 12 ohm A m p = E / I = 1 2 v / 1 2 o h m = l a m p Voltage drop of series, E = I x R, 1 x 8 = 8V Voltage drop of parallel, 1 a x 4 ohm = 4 volt Amp flow through each bulb I = E/R

I = 4v /20ohm = .2amp Total amp flow through bulbs

.2 amp x 5 bulbs = 1 amp

INSTRUMENT PANEL LIGHTING PARALLEL CIRCUIT DIAGRAM

F U 5 E HEADLIGHT

RHEOSTAT

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DIODES

Diodes are devices which will allow elec- tricity to pass through in only one direc- tion. DIODES are simply a ONE WAY VALVE. They allow current to pass through in one direction and if the cur- rent tries to reverse direction, then the diode will block current flow.

Alternators use nine diodes. Six diodes are in the rectifier bridge and three in the diode trio. These diodes turn the spin- ning action of the alternator and its alter- nating current (AC) into direct current (DC). If any one of these diodes fail, performance of the charging system will be greatly affected.

LIGHT EMITTING DIODES

Light Emitting Diodes or LED's are used frequently in many automotive applica- tions. They are built like a regular diode only they are designed to produce light . Whereas a regular diode made from sili- con will require about .6v to turn on and pass current, the LED needs 1.5 to 2 . 2 ~ in most applications. LED's are just like regular diodes because they will not pass current that wants to go against it.

DIODE ELECTRICAL SYMBOL

DIODE CURRENT FLOW

LIGHT EMITTING DIODE

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X X X X X X

WOUND STATOR

SINCE ALL THE CiJRRENT I CONVENTW NAL MUST PASS THRGUGH THE CENTER CONNECTION LESS OUTPUT RESULTS

Y 5TATOR

ALTERNATOR OPERATION THROUGH EACH PHASE

TRACE CURRENT FLOW THROUGH DIODE BRIDGE IN EACH DIAGRAM

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Diodes are also used to "bridge" sole- noids. Review of the information on ignition systems shows in detail how the primary coil builds up a strong electrical field in the secondary coil, enough to fire the spark plug when the primary coil is turned off. This condition is normal for the many electrical coils and solenoids in the car.

Of special concern are the coils con- trolled by the ECM. Diodes are placed across many coils. They are installed in a "reverse bias" position to block B + and therefore the current passes through the coil. When B + is turned off the magnetic field of the coil collapses inducing cur- rent flow in the coil. This current then passes through the diode, since this cur- rent is headed in the same direction as the diode arrow, which was previously blocking B+ and thus this current flow induced by the electric field of the coil is allowed to "collapse upon itself'. A spark is not produced and the delicate ECM is protected against damage.

Even small coils, found in simple relays, can produce over 100 volts when they are turned off. Large air conditioning clutch coils can produce 60v to 130v with much greater amp flow. Higher voltages are produced with quicker clutch return times. You will see this despiking diode connected to and taped over, on the elec- trical plug attaching to the ac compres- sor.

A / C COMPRESSOR CLAMPING DIODE

CURRENT CONTINUES TO FLOW THROUGH THE CLAMPING DIODE UNTIL THE COMPRESSOR FIELD

COLLAPSES UPON ITSELF

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Transistors are simple little devices when you understand how they do in fact work. The best way to understand them is to first look at a simple old light switch on the wall. You flip the switch up and the light goes on. You flip it down and the light goes off. Now if I tell you that the transistor works exactly the same way as the light switch, only electrically, and that instead of manually pushing the switch you need only send a little voltage to it in order to turn the light on, then we've almost got it licked.

Look at the diagram on the NPN transis- tor. Notice that the main current path is from top to bottom. Coming in from the side is the small current path necessary to turn on the large current flow. This means that you could use a very small and light duty switch to turn on a high current requirement accessory. It only takes .6v to turn on the average transistor.

Transistors function as switches and they can function as a flow control valve. Now that we have the transistor turned on, if we want to let more current flow through it, top to bottom, then we simply apply more voltage to the base. When the transistor is at "saturation" it is allowing all the current through it is designed for. Drive it beyond saturation and it will be destroyed. 9,000 rpm with your street motor won't work. However, a little voltage change on that base lead will be just like your foot on the accelerator.

N P N TRANSISTOR

NPN TRANSISTOR

Nclativc POSI~~VC Ne jativc

Semiconductor nternal cm~tructim

P N P TRANSISTOR

R PNP TRWSTOR

F L

Semiconductor internal construction

A SMALL CURRENT IN THE BASE LEG WILL TURN THE

- I

Page 27: 61689121 Automotive Engine Electronics

POINT SET

- - - ---------- ----------

POINT TYPE I G N I T I O N SYSTEM

out over early magneto systems. If you understand how the point system works you will be able to service millions of different cars, but they all work the same, even if the actual components are differ-

Point type ignition systems were the stan- dard ignition method for cars by winning

ent.

Refer to the picture and find the 12 volt

little resistance to current flow, but when the current does flow it sets up a

source. Let's follow our current through the system and see what actually goes on.

First the current flows through the Pri- mary Ignition Coil, which is composed of large diameter wires to allow lots of amps through. If you were to check a primary ignition coil with an ohmmeter you will probably find about one ohm of resis- tance. One ohm means that there is very

large electromagnetic field around the coil (see page 13). This electromagnetic field is essential to the operation of the coil because it will induce current into the Secondary Ignition Coil later on, but for now this magnetic field is just building up in strength.

Now that the current has passed through the primary coil it heads onto the Contact Point assembly. In fact it goes all the way to the Top contact point, as shown in the diagram. The top contact point always will be hot. If you took a voltmeter and touched it to the top point you would see 12 volts.

If you have ever installed or held a set of

Page 28: 61689121 Automotive Engine Electronics

points you know that there is a spiral spring used to bring the contact points together. In order to separate the points the rotor lobes must be positioned, in relation to the rubbing block on the point locator arm, so that the points will alter- nately open and close as the rotor turns.

Since the top point is always electrically hot, whenever the points come together current will flow across to the bottom point and thus to ground completing the circuit. Many amps will then flow through the primary ignition coil rapidly buildingtheelectromagneticfield around both primary and secondary coils.

Since the rotor is generally driven by the camshaft it will continue to turn. A lobe of the rotor will begin to rise, eventually pushing the top point away from the bottom point. At that time the primary coil will be turned off since current can no longer flow through the primary coil.

The Electromagnetic Field which was built up around both the primary and sec- ondary coil will start to collapse. This field is made up of "magnetic force lines" which will start to fall back upon the primary coil. These lines of magnetic force will attempt to push current through the primary coil to keep the current flowing ... sort of like lifting your foot off the gas while driving at 50 mph, the car will continue to coast since you have already built up speed and momen- tum.

These magnetic lines of force try to do the same thing only electrically. However, in

27 the process of collapsing they cut across the secondary ignition coil winding and begin to induce electrical pressure in this coil. The secondary coil can have 6,000 to 14,000 ohms resistance which means that it is a very long coil of wire and the collapse of the electromagentic field will cut across a lot of wire length.

This is exactly what happens and the electrical pressure built up in the secon- dary coil becomes so great that it will eventually jump a large air gap. The air gap of course will be on our spark plug, igniting the engine air fuel mixture at just the right time to make for good power and driveability.

CAPACITOR

This is a good time to look at the "electri- cal shock absorber" or capacitor. Let's go back to the primary ingition coil for a minute and look at what's happening. When the contact points close current passes through the primary coil and on through the contact point set to ground. When the points are pushed apart the circuit is broken and the electromagnetic field will start to collapse inducing elec- trical pressure strong enough in the sec- ondary coil to fire the spark plug. What about the primary coil ... it will have an induction also ....

Imagine the points just opening, many electrons will be hurriedly moving along; just like that car at 50 mph. Your car might "stop on a dime" but I would guess that a lot of skid marks would result if you locked up the brakes all the way to a

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28 "dead stop," then you would need to go buy some new tires because of the flat spots. If you haven't tried this just ask some of the guys at your service facility; I'm sure that there is someone there who has destroyed some perfectly good tires by locking up the brakes. Of course the best way to stop is to use the brakes, that's why a car has brakes.

Electricity flowing in the coil needs a way to stop without "crashing out." Such is the job of the capacitor, it provides a "run off area" or another path for this electric- ity to go. Have you ever been to the mountains and noticed "truck run offs" which are large sand pits that 18 wheelers can head into if their brakes quit while going downhill. A capacitor is exactly the same thing, an electrical run off with no escape other than go back out the way the current originally came in.

When the points close many electrons will start moving. When the points open these electrons will build up tremendous pressure on the top point as they all try to keep on moving. If we add a capacitor then the electrons will electrically take the capacitor for ground and head off into the capacitor. A capacitor is a "false ground" in this application because the electrons cannot actually get to ground they only think that they can. The capaci- tor will use a large internal surface area or "plate" wrapped up inside it, posi- tioned very close to another "plate" which is attached to ground. Thus the electrons think that they can get to ground by going through the capacitor. As more and more electrons enter the

capacitor it will build up electrical pres- sure and start to build up resistance to the other electrons which are also headed into the capacitor. When the electrical pressure gets higher than that of elec- trons trying to get in, then electrons will flow back out of the capacitor. Thus the similarity to the shock absorber give-and- take.

If you have ever wondered about those bumpy little lines on an ignition oscilloscope ... well now you know. Those funny lines are the electrons bouncing back and forth because of the capacitor. If the capacitor is bad then you will burn out the points because instead of just sparking the spark plug you will also spark the points and they will simply burn UP.

Capacitors are used in many applica- tions. They reduce alternator hum in the radio. They are used any place that electrical pressure (voltage) fluctuates and you need to smooth things out. Nothing is supposed to go through them, unless it's been blown out. They normally seem to work quietly and forever ... until it quits and something burns up.

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4 CYLINDER MAGNET I C

TRANSISToR PICKUP C O I L

12 I - VOLT

4 H E I

HIGH ENERGY I G N I T I O N SYSTEM

Now that we know how a set of points work we can move into HE1 which is really a logical progression of ideas and technology. In review, we know that the points close allowing the primary coil to build up an electromagentic field which collapses when the points open inducing electrical pressure (voltage) into the secondary coil which causes the spark of the spark plug.

HE1 works the same except that a tran- sistor is used instead of points. Since the transistor is electronic it won't burn up like a set of points. I didn't say it wouldn't burn up, I'm sure that you can destroy anything but that's not the point. Anyway, the idea is that a transis-

tor will not need as much attention or maintenance as the points. Now all we have to do is turn the transistor off and on and everything will be great.

If you haven't read the section on transis- tors stop here and go do it. This book is designed with the KISS method, meaning Keep It Simple Stupid and your author thinks that you better understand how this mess works with the easy stuff first. I didn't say-I was easy, I said that it was going to be explained simply. If you do not under- stand how point ignition systems work or you do not understand how the transistor works, then do yourself a favor and go back to these systems now for review. HE1 can be simple but it will only be simple if

Page 31: 61689121 Automotive Engine Electronics

30 you understand the basics. Have you ever seen a 440-T4 transmission pulled all the way down? It will cover every workbench in the shop. I can overhaul a turbo 400 but I would not even want to think about the 440-T4. What does this have to do with HEI? As a wise man once said (he was with the World of Outlaws, the sprint car association) "if you're going to run with the 'big boys' you better come pre- pared." Moral of the sto ry... don't try to fix something you don't understand and you can't fix something that's not broke.

In order to make the HE1 transistor work all we need do is to provide it with a small voltage to turn the primary coil on. This small voltage comes from the Magnetic Pickup assembly which now replaces the rotor of our point ignition system. Have you ever noticed how magnets react to each other? Either you cannot pull them apart or you cannot push them together, no matter how hard you try.

Now we've got HE1 licked. Put a star magnet on the distributor shaft and put a magnetic ring outside it. When the dis- tributor shaft spins the magnets will pro- duce an alternating current. Take this current and pass it through a diode and now we have pulsating DC because half the original AC is blocked. Now add the Zener diode and we have a nice square wave produced which will make that transistor work just like a set of points.

To get the HE1 right for your engine the magnetic pickup needs to have the same number of star points as the number of cylinders in your particular engine.

L- 4 Terminal HE1 Module

Therefore: 4 star = 4 cylinder, 6 star = 6 cylinder, or 8 star = 8 cylinder.

If this explanation makes sense to you then you will be well prepared to deal with any electronic ignition system. Making the primary coil work will be the function of a power transistor. Making the power transistor work will be a func- tion of some sensor. The pickup sensor may be magnetic, hall effect, or optical. However there must be some sort of pickup mechanism. Once you have the general electronic ignition system fig- ured out you should be able to diagnose most problems by referring to specific information provided by the manufac- turer of the subject ignition system.

Remember, what we are dealing with in this book are general concepts which will help you diagnose problems. This type of information is universal and therefore it can be applied each and every day to your work. You have special tools in your tool box which you seldom use. This informa- tion is valuable each and every day as you approach new problems. To fii the car is one thing. To understand what was wrong with it and then be able to fi it is much more difficult.

Page 32: 61689121 Automotive Engine Electronics

- - I

---------

REFERENCE - - I

EST 5 VOLT BYPhSS H IGH ENERGY I G N I T I O N SYSTEM WITH ELECTRONIC SPBRK T I M I N G

With advent of the on board computer or ECM, mechanical and vacuum advance could be eliminated. The computer could simply look at its sensor values and determine what it wanted to do with ignition timing.

In order to get this system to work we simply change the routing of the signal from the original HEI. When the engine starts the HE1 works like normal, as we have looked at, with the magnetic signal going to the transistor to operate the primary ignition coil. When the engine reaches 500 rpm the computer will apply

5 volts to energize the bypass coil. The bypass coil pulls the relay control arm over to the Electronic Spark Timing contact and this signal is then fed to the power transistor.

Inside the ECM there is a signal linking between reference and EST. Hence, when the reference signal is received the ECM knows to send out an EST signal. If reference is lost the engine will stop running. Why? Send no signal to the ECM and it will think that the engine is not running so no signal will be sent out to the power transistor.

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Engine Starts on Base Timing

ECM

EST

Rclcrcncc -)

Bypus

Ground

h . 1

During crank and until 500 rpm the engine runs on Base Timing, just like standard HEI.

Enginc Runnin j Wi th E S T

ECM

EST t

Rcfcrcncc -)

Bypass ?= Ground

1

At 500 rpm the ECM sends 5 volts down the bypass. This switches timing control to the ECM and Electronic Spark Timing is engaged.

During the 1982 model year GM ignition modules for this type of ignition system began incorporating an internal resistor at the end of the EST contact. This was done so that the ECM could send a circuit checking voltage down the wire before EST was engaged. Otherwise, if the EST circuit was open or shorted to ground the engine would stall when EST was cycled on by the ECM. This circuit check is now performed before EST is engaged. Be- fore this feature became standard the en- gine would stall when EST was engaged. This start and stall cycle would happen repeatedly. On carburetor equipped cars

you could disconnect the 4 wire connec- tor of the distributor and the car would continue to run because then the 5 volt bypass signal would not be applied to the module.

On EFI' and PFI cars if you jumper to- gether the A to B connectors in the ALDLyou should notice a change in rpm to show you that the EST is working. GM diagnostics say to do this at 2,000 rpm but you can notice the rpm difference at idle. Do not drive the car with A to B jumpered together, you can burn the car up. For more on this subject refer to the scanner and how it affects the car.

Page 34: 61689121 Automotive Engine Electronics

You really don't need a distributor, you only think that you need it. Let's think about this a minute and maybe it will not seem quite so bad. At first it really bothered me that the distributor was gone but then I realized that it wasn't any good to me and that if it was eliminated then I would have one less thing to take up space on top of the engine.

As for the basic idea, well let's start with the distributor shaft. It is powered by the camshaft. With the pole piece creating the control signal for power transistor of the HE1 module. If a Hall effect sensor were hooked to the harmonic balancer then the spinning crankshaft would give us the best indication of exactly where the crank is. However, since the crank goes around twice for every revolution of the camshaft we must fire two cylinders at the same time in order to get the engine working properly, which is how it works.

The only trick is to get the coils started off in the right sequence and then the elec- tronics will keep everything working right. This initial signal can come from several places such as using a double Hall effect sensor on the balancer with one having only one vane to electronically signal the start up sequence and then the regular vaned sensor can provide the control signal to operate the coil packs.

For many six cylinder engines a 3 vaned rotor is mounted on the back side of the harmonic balancer. When these vanes pass through the Hall Effect sensor a square wave signal is produced. Each vane is dedicated to only one coil pack which will fire two spark plugs at one time. The cylinder on compression and the cylinder on exhaust.

SWARE WAVE PRODUCED BY W EFFECT SYSTEM

\ FIXED POSITION . - 1( MAGNET

- -

This start up signal could also come off a Hall effect sensor mounted on the timing gear since it would also identify where to start and then the crank Hall effect would take over for crank position.

These crank generated signals provide the same information to the ECM as it would receive from the magnetic pickup in a standard HE1 only now we do not need the distributor to generate these signals.

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c31 COMPUTER CONTROLLED COIL IGNITION

3 VANES ARE MOUNTED ON THE BACK SIDE OF THE BALANCER EACH VANE CONTROLS ONE COIL

SQUflRE WflUE PRODUCED BY HflLL EFFECT SENSOR I S SENT TO THE ECN I S ENGINE REFERENCE SIGNIL

Page 36: 61689121 Automotive Engine Electronics

Federally mandated Corporate Average Fuel Economy or CAFE standards set minimum emission requirements and fuel economy requirements. GM deter- mined that the traditional carburetor system could no longer get the job done of controlling the air / fuel mixture. Computer Command Control or simply CCC could adequately meet these legal standards. CCC put a computer in the average automobile.

A small on-board microcomputer was selected to perform the task of keeping watch on the air / fuel mixture. Specifi- cally, this microcomputer called an Elec- tronic Control Module or simply, ECM is intended to watch what happens in the exhaust pipe and use this reading to meter fuel into the engine.

The basic principle is straightforward. Monitor engine exhaust in order to con- trol fuel delivery. This is the operational principle behind every automobile manufacturer's system relating to air / fuel control in order to meet applicable fuel and emission standards.

In order to make this control system work it seems that just about everything under the hood and on the engine had some sort of computer wire coming out of it. Making a carburetor into a precision metering device seemed like a good idea at the time.

CCC Carburetor is an expensive and com- plex device. Special training and special tools are necessary before making any adjustments to this type of carburetor.

A regular carburetor (no wires coming out of it) will have metering jets or orifice to allow fuel to pass through in order to get into the airstream going into the. engine. CCC carburetors can control fuel flow through the jets.

CCC carburetors (look for the wires) have a Mixture Control solenoid or MC solenoid inside the carburetor which can be turned on and off by the ECM. When the MC solenoid is turned on fuel deliv- ery is restricted and the engine will run lean. When the solenoid is off the engine will run rich. Pulsing of the MC solenoid is the sound you hear coming from under the hood of the car when you turn the ignition key on.

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Let's look at what happens when the MC solenoid is energized so we can under- stand exactly what the ECM is trying to do. First off, the solenoid runs hot, meaning that it is wired to B+ and then all the ECM needs to do is ground the wire and the solenoid will be energized. This ECM controlled switch is called a "Driver" or "ECM Driver".

When the ECM grounds this circuit, current flow energizes the MC solenoid. An electromagnetic field is developed. This field pulls down a metal plate, about the size of a postage stamp, mounted just above the solenoid inside the carburetor. This plate is normally held up by a high

' quality spring.

When the plate comes down two things happen. Fuel is reduced because the metering rods are pushed down into the main metering jets and an idle air bleed is opened which allows air access be- tween the idle tube and a fuel channel restriction. In simple terms ... when the solenoid goes on fuel is reduced and air is dumped in.

This combined action will make a big difference between rich and lean condi- tions and gives the ECM a wide range of control over engine operation. This book will not attempt to get into specific ad- justments for any carburetor, only to provide a general theory of operation. Overhaul and adjustment of carburetors is a science by itself.

An oxygen sensor is placed in the exhaust

Close up internal view of CCC carburetor. Clearly visible are rich and lean stops for Mixture Control (MC) solenoid. MC solenoid is energized in this picture.

gas stream so that it can get a reading on the amount of' oxygen in the exhaust gases. AN OXYGEN SENSOR SENSES OXYGEN. An oxygen sensor is a voltage generator, it makes voltage chemically ... that is correct. The oxygen sensor is a sophisticated device which uses several exotic metals which will produce electricity when heated in the presence of oxygen.

Let's look inside this sensor. It screws into the exhaust so exhaust gasses can pass over the face of the sensor. The sensor is hollow so that normal air can get to the inside of the sensor. When the sensor gets hot a voltage is produced because of the difference in oxygen con- tent of the two air surfaces.

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For instance, if the sensor were simply hot and hanging out on the end of a rope in the middle of the shop then the oxygen content of the air inside and outside the sensor would be the same with no differ- ence in oxygen content, thus no voltage. Now back to the car. With exhaust gases going over the sensor there is a difference in oxygen content between the two air masses. If you add more fuel you will have less oxygen in the exhaust stream because it will have been burnt up in the combustion process. If you remove fuel then you will have more oxygen in the exhaust stream. The greater the differ- ence in the oxygen between the two then the greater the voltage produced.

Oxygen sensors are designed to produce voltage over a range of .l to .9 volt. They are designed with a .45 volt mid range or center. If a voltage greater than .45 is produced the engine is said to be rich, all the oxygen has been burnt up. Less than .45 volt and the engine is lean, because there is a lot of oxygen in the exhaust stream which has not been burnt up.

The ECM will adjust the on time of the MC solenoid so that the oxygen sensor voltage "toggles" or pivots around .45 volt. If the ECM cannot do this job properly then the Check Engine or Serv- ice Engine Soon light will come on and a Code will be set for the rich or lean condition which the ECM cannot cor- rect.

THE OBJECTIVE 15 TO MAINTAIN OPTIMAL AIR I FUEL RATIO FOR : 1) EMISSION CONTROL 2) FUEL ECONOMY m

I I I I I I I I I I I I I I I I I I I I I I I I

1 1 1 1 1

I n I I I I I I I I I I I I I I I I I

I I I I I I I I I I I I

0 1 5 : I : @

I I I I I I I I I I I

I I I I I I

Page 39: 61689121 Automotive Engine Electronics

THE OBJECTIVE 15 TO MAINTAIN UP'TIMAL AIR I FUEL RATIO FOR : 11 EMISSION CONTROL 2 ) FUEL ECONUMY

Electronic Fuel Injection is one of the best systems to come along in the history of automotive technology. It is simple, precise and reliable. EFI is a "single point" fuel delivery system meaning that all the fuel to the engine is supplied from a central location by one or two fuel injectors.

Using the reference signal to the ECM provides accurate information about crankshaft position and engine rpm. Each time the ECM receives a reference signal the ECM will pulse the fuel injec- tor. This means that short pulses of fuel are delivered into the intake manifold at the same point as the carburetor used to be placed. Each pulse of fuel will be metered to provide the necessary fuel for each cylinder needing an air and fuel charge.

If you take a timing light and hook it to the ignition coil wire you can see the fuel

CADILLAC HT-4100 USES A DUAL THROlTLE BODY FUEL INJECTOR.

IN,IECTORS FIRE ALTERNATELY WHEN REFERENCE SIGNALS ARE RECEIVED BY THE ECM.

Page 40: 61689121 Automotive Engine Electronics

pattern delivered from the fuel injector. If you push the Throttle Position Sensor or TPS down with the timing light in- stalled, you will see extra pulses of fuel being delivered since the ECM interprets this action as acceleration. Since you do not have an accelerator pump then you will need this extra fuel to prevent a possible tip in hesitation. If you put a vacuum pump on the Manifold Absolute Pressure sensor or MAP sensor you can cause the engine to stall because fuel delivery can be cut back or cut off en- tirely. The ECM will interpret this high vacuum as high deceleration with closed throttle.

If you spend time around the circle track you know that carburetors have to be rebuilt several times a season because the gaskets are simply sucked into the carbu- retor. Imagine how the racing carburetor will go wide open down the straights and then at high rpm have the throttle valves snapped shut as the car slows for the corner ... lap after lap. The ECM says that with high vacuum in the intake manifold and with low TPS voltage that you do not need fuel, so the injector is simply not turned on at all.

EFI generally works in a Synchronous mode, meaning that for every reference pulse you get a shot of fuel. However, it can also work in an Asynchronous mode under acceleration or deceleration when synchronous fuel delivery just will not do the job right. Another example of asy- chronous fuel delivery occurs with Prime Pulses which occur on some engine sys- tems. Prime pulses occur with a cold

DUAL THROlTLE BODY INJECTORS ARE USED ON MANY DIFFERENT TYPES OF 6 AND 8 CYLINDER ENGINES. ALL SYS- TEMS WORK VERY SIMILAR. THE DUAL THROlTLE BODY "CROSSFIRE" ALSO ALTERNATELY PULSES EACH INJECTOR.

AIR LEAKS CAN RESULT IF THE TOP "0" RING LEAKS. FUEL LEAKS CAN RESULT IF THE BOlTOM "0" RING LEAKS.

engine to get it started. Since you do not have an accelerator pump to provide that extra fuel to get the car started in cold weather prime pulses will be delivered before you start cranking to get fuel into the engine. The ideal airlfuel ratio for the engine is 14.71b of air to 1 lb of fuel when the engine is warmed up. When the engine is cold, 20 below zero, then 1.5 to 1 is the ratio. Carburetors have chokes, EFI likes asynchronous prime pulses.

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Port Fuel Injection is the most precise fuel metering system used in today's automobile. Fuel is metered independ- ently to each cylinder in this system. A fuel injector is mounted in the intake manifold so that it will spray fuel directly on top of the intake valve. This method gives the highest degree of response and increases both performance and econ- omy.

Fuel injectors can be pulsed on together or sequentially. Most systems pulse each injector on every revolution of the crank- shaft. This means that an injector must be turned on twice in order to deliver the correct amount of fuel for each intake cycle. Sequential systems deliver the full fuel charge when the intake valve is open so that the engine will use this amount of fuel for the next compression and power stroke.

It is important to remember that fuel travels from the in-tank mounted fuel pump, through the fuel rail and to the fuel pressure regulator. The fuel pres- sure regulator has a connection to the in- take manifold with the objective to main- tain about 35 psi across the injector throughout engine operation.

Although EFI and PFI fuel pumps look basically the same they are not. EFI uses a twin turbine generating about 12 psi. PFI pumps can generate 60 to 90 psi.

PORT FUEL INJECTION SYSTEMS USE AN INDIVIDUAL FUEL INJECTOR FOR EACH CYLINDER. BUCK GRAND NATIONAL TURBO SEQUENTIAL SYSTEM SHOWN ABOVE. 3.8 MFI SYSTEM BELOW.

There is an internal relief valve in the I I pump if a fuel return line were to become ( I restricted producing high fuel pressure.

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PFI THROlTLE BODY ASSEMBLY

THROTTLE

I A C

PORT FUEL INJECTION

PRESSURE REGULATOR INTAKE MANIFOLD

VACUUM / PRESSURE

FUEL RETURN I # 1, TO TANK

SPRING

COLD START INJECTOR Cold Slarl Injecioc is mergized to provide extra luel when lhermo- lime 4 t h is closed.

TO STARTER CRANK FUSE SOLENOID Cold dort injeclor is

no1 found on all q ines .

I I is only enerqized when the crank motor is energized.

I THERMO TIME SWITCH

8 SECONDS MAX COLD START VALVE

Page 43: 61689121 Automotive Engine Electronics

PORT FUEL INJECTION

FUEL SYSTEM

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Sensors provide the ECM with vital in- formation necessary for the job of main- taining proper air / fuel ratio. Just as most people have the senses of: sight, hearing, touch, smell, and taste; theECM needs its sensors also. Just like people, if the ECM loses a sensor it can continue to operate but it's performance will be impaired to a certain degree. This state- ment being true with exception to the reference signal. If that signal is lost then the fuel injected car will not run.

At this point in our study of the ECM controlled automobile several things need to be stated. First off, we have already covered the basic principles of engine operation for fuel injection. This being that the engine receives fuel from fuel injector(s) based upon a controlling signal from the ECM. A decision is made by the ECM to inject fuel based upon engine rpm and engine load.

If you understand this relationship be- tween ECM and fuel injectors you are well on your way to success with the fuel system. Do not forget that an in-tank fuel

ump pressurizes the fuel system. TBI Re1 pressures would be between 8 to 12 psi. PFI fuel pressures range from 28 to 42 psi, with turbocharged engines reach- ing 50 psi.

In your diagnosis of the fuel system you need to check 1) fuel ressure, 2) how much fuel is injected, 3 7 wiring harness,

and 4) injector resistance. Although this detailed procedure is designed for PFI it also applies to EFI. Included in this book is a "Fuel Injector Test Procedure." Reference and use this testing proce- dure. If you do use it, you will quickly be able to determine if you do in fact have a fuel problem.

Remember that this book is written for you, the fellow turning the wrench. You do not get paid to diagnose. You get paid to fix. Way back in the old days it was: 1) fuel, 2) ignition, and 3) mechanical prob- lems which occurred. Today there is 4) electronic. You must know which area to look in before you can fix the car. If you think the car has a fuel problem run the test. If you run the test you will know whether or not you in fact have a fuel related problem. If everything checks out then proceed on to areas 2), 3) and 4).

Now that you're a professional 1) fuel expert {and you will be if you use the test!) let's move on into area 4), the electronic domain. Before we do ... let's see ... 2) has already been covered and 3) ... well if you feel unsure about general mechanical then you better take some classes or read a ood book. If you insist upon using 1/2" f rives on 114" bolts then this book is not for you.

In summary, the fuel injection system is very tough in the beginning. However, since injection is a precision fuel meter- ing method it can be checked and evalu- ated in a logical and orderly way. After you do check it you do not need to re- check it.

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One of the most important sensors is the Throttle Position Sensor or TPS. This device provides the ECM with a signal concerning where your right foot is. Are you accelerating, decelerating or main- taining speed? The first indication of change comes from the TPS. Your input to the engine is through the accelerator pedal, which just happens to be con- nected to the TPS.

The sensor is attached to the side of the throttle body and is actuated (moved) by the throttle shaft going through the throttle body. When your foot moves the accelerator cable and opens the air valve the TPS is also moved. This movement tells the ECM that you are accelerating and that extra fuel is needed.

Inspection of the TPS reveals that it has a 3 wire connection. One lead is a 5 volt input from the ECM. Another lead is a ground. Between these two outside leads is the TPS signal for the ECM. Internally the TPS is a rheostat capable of giving the ECM voltage changes in thousands of a volt!

THROTTLE BODY

THROlTLE POSITION SENSOR (TYPICAL TYPE D I A G M )

AorC j

Page 46: 61689121 Automotive Engine Electronics

TPS CHECK

A TPS sensor is designed to provide throttle position voltage to the ECM. We will check this voltage to check sensor operation. Insert jumper wires or use the CHAT tool. A scanner will give you a voltage reading if there is voltage coming back but it is not accurate enough if your problem car has a hesitation or surge driveability problem.

There are three wires and we need to check each of them. Use a high imped- ance digital multimeter such as the Kent Moore J34029A or equivalent for all tests.

Test 1. Input power to TPS of approxi- mately 5 volts. Test 2. Ground wire has proper continu- ity. Test 3. TPS voltage signal output. Ini- tially check with multimeter on 20 DCV scale for maximum Wide Open Throttle (WOT) voltage. Do not be alarmed if it will only go to 3.5 v., on some cars this might be the case but generally 4.5 will be the high reading. Return throttle to idle. Set DMM on 2 DCV scale. You should get readings in .001v. changes. If you get erratic or jumpy voltage changes then your TPS may be deteriorating or coming apart inside. You may need to use a small screwdriver to move the TPS control arm for voltages up to the meter limit of 1.99%. With practice you can get the TPS to give voltage readouts in thousands (.001) of a volt.

I \ h I

TPS SENSOR E

t C M

DIGITAL MULTIMETER

TPS VOLTAGE CHECK

Remember, if TPS voltage changes the ECM will think you want to accelerate or slow down. When a TPS starts to deterio- rate and flake apart internally erratic high and low voltages will come from the sensor. The rheostat is electrically con- ductive. When it comes apart and you have an electrically conductive "dust" you will get jumpy voltage readings.

Cars which have the EGR near the TPS experience a higher degree of TPS fail- ure. Any time you see these two close together check very closely because of the heat which comes off the EGR has traditionally been very hard on TPS sen- sors.

Page 47: 61689121 Automotive Engine Electronics

Coolant temperature sensor provides a signal to the ECM which is used for fuel delivery calculation and other tempera- ture related functions. Temperature readings are provided by a circuit which uses a thermistor which is a specialized resistor that changes resistance accord- ing to temperature.

A signal voltage is sent to the coolant temperature sensor from the ECM. The ECM will then interpret this signal as engine temperatue. When the engine is very cold a high voltage reading will be observed. As the engine warms up the thermistor resistancewill drop and so will the signal voltage. At normal engine operating temperature the voltage read- ing will be between 1 to 1.5 volt.

If the coolant temperature sensor were to go open or the signal voltage wire to it were to become open the ECM would see high voltage. High voltage would be interpreted as very cold conditions. Very cold conditions would mean lots of fuel for "choke" type conditions. It is possible that the engine would be over fueled and could not start under these condtions.

Manifold air temperature sensors tell the ECM what temperature the incoming air is. This reading is used in the fuel ratio calculation. MAT sensors can be mounted in the air cleaner assembly or in the intake manifold.

Coolant Temperature is used by the ECM to Control:

* Fuel Delivery

Coolant Temperature may be used by the ECM to Control or Modify:

* Electronic Spark Timing * Idle Air Control * Exhaust Gas Recirculation * Canister Purge * Cooling Fan * Electronic Spark Control

THERMISTORS CHANGE RESISTANCE WITH

I I

TEMPERATURE

I I

I C GROUND - ~1

k-

COOLANT TEMPERATURE TO

COOLANT TEMPERATURE SENSOR READINGS

O h m s Resistonce

185 4 50 1,800 3,400 10,000 13,500 25.000 100,000

Degree F

21 0 160 100

7 0 32 20

0 -40

Deg ree C

100 7 0 3 8 20

0 -7 -18 -40

Page 48: 61689121 Automotive Engine Electronics

An automobile engine is an air pump. Whenever the intake valves open a cer- tain amount of air enters. If you have a turbocharger there will be boost pressure applied which will force even more air into the cylinders. The faster the engine spins over the more air you move, thus the need for better intake, cylinder head and exhaust design.

In order to make the most power and have optimal economy the ECM must know just how much air is entering the engine. Manifold Absolute Pressure or MAP sensors are used to provide this information. At sea level atmospheric pressure is about 30 inches of mercury and decreases about one inch per thou- sand feet of elevation. Therefore, at Denver the "Mile High City" atmos- pheric pressure would be about 25 ifiihes of mercury. A car in Denver would not have as much air entering its cylinders and would not make as much power. If the same amount of fuel were to be in- jected then the engine would run rich.

MAP sensors tell the ECM how much pressure will be moving air into the cylin- ders. A silicon chip is diaphragm mounted so that it will flex according to the applied intake manifold absolute pressure. Chip deflection is electrically transmitted to the ECM so that an accu- rate pressure is provided for fuel calcula-

Manifold Absolute Pressure sensor provides ECM with reading on how much air enters the engine.

Barometric pressure sensors are used so that the ECM will always know what atmospheric pressure is. However, it became evident to GM that under wide open throttle conditions intake manifold pressure was the same as barometric pressure sensor readings. This fact led to the elimination of the barro sensor be- cause the ECM was reprogrammed to accept engine crank and wide open throttle MAP readings for barometric pressure. Whenever you start the car a MAP value is taken and whenever TPS voltage indicates WOT the MAP value is

tion. I updated.

Page 49: 61689121 Automotive Engine Electronics

The knock sensor provides an electrical input when spark knock occurs. This

Electronic Spark Control is a system designed to provide the ECM with infor- mation concerning engine detonation or spark knock. A piezoelectric knock sen- sor is screwed into the block and it pro- duces voltage when vibrated or shook at the frequency of spark knock. This signal is used by the ECM to retard spark timing of the Electronic Spark Timing program.

input will turn on a transistor and thus takes away the voltage signal the ECM should be receiving from the ESC Mod- ule. When the ECM notes that the input voltage has dropped, spark timing will be quickly retarded.

ELECTRONIC SPARK CONTROL

After timing has been retarded, up to the limit of 20 degrees, timing will gradually be brought back up to the value the ECM would like. Timing can be retarded at the rate of 2 degrees per second and it can be advanced at the rate of 1 degree per second.

It is possible for the knock sensor to produce voltage when things other than timing shake it at certain frequencies. Connecting rods, piston slap, bad bear- ings, loose sheet metal and just about anything else which can make a good "rap" will set it off. Also, if the ESC wire leading to the ECM accidentally gets near a spark plug wire voltage could be induced into the ESC wire from the igni- tion system.

I IGN B+

ESC SIGNAL E C M

1 l 1 - - - - - - - KNOCK

ESC MODULE SENSOR

~iezoelectfic Knock Sensor is screwed into the block and produces a voltaga when

spark knock vibrations occur.

Screw the knock sensor into the block to 14 ft/lb of torque, with antisieze applied to the threads. Over torque and it would be like trying to wear a pair of shoes one size too small ... whenever you put your foot down ... OUCH ... all day long.

If the wire comes off the sensor, the engine could be damaged because the ECM would not receive the warning sig- nal from the sensor.

Page 50: 61689121 Automotive Engine Electronics

Mass Air Flow or MAF sensors are very accurate devices designed to measure the mass of the incoming air to the engine. When the temperature is low air be- comesvery dense. When air is hot it is less dense. Fog staying low to the ground or warm thermals rising are examples of dense and light air.

Optimal air / fuel ratios are based upon weight (mass x gravity) and not upon volume. Want a quick test? Take a Coke bottle and put it in the freezer until it is cold. Put a balloon over the bottle's mouth. Set the bottle out in the sun. This will be a good example of how air ex- pands when heated.

Two types of MAF sensors are in use. Most common is the metal foil sensing element using a postage stamp size sens- ing element and a temperature sensing thermistor. The metal foil sensing ele- ment is heated above the temperature sensor and the amount of heat required will allow the ECM determine air mass. On 5L and 5.7L V-8 a hot wire MAF is used. A small wire is cooled by air flow. This value is used to determine air mass.

If the MAF tells the ECM that no air is flowing the engine will run rough because of a lean condition. If it tells the ECM the air is dense a rich condition can exist.

Incoming air passes over the air temperature sensing thermistor, through an air direction tube and over the metal foil sensing element.

Carefully inspect the metal foil sensing element. If the two metal layers separate an air pocket will be formed around the ceramic coated wire sandwiched be- tween the foil layers. Air will insulate the wire so less energy is required to maintain wire temperature which will cause the ECM to deliver less fuel than the engine needs. This can be a major problem before the engine goes into Closed Loop operation.

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EGR Systems Operation

Exhaust Gas Recirculation or EGR is one of the most misunderstood engine systems. If you had a way to change engine displacement, get better fuel economy, and reduce emissions all at one time that would be good. EGR does that for you.

I realize that you hate EGR, everyone hates EGR, right? It's just what you've heard since there was an EGR. Let's look at this technically for a minute and then if you still hate it ... well, then that's up to you.

When a piston goes down, air and fuel are sucked into the combustion chamber. A strong vacuum is created. If the throttle valve were opened the vacuum would go away and you would have atmospheric pressure blasting into the combustion chamber (review the MAP sensor if you need to). The engine has to work very hard to make that vacuum. It takes en- ergy to do it. If you could reduce the vacuum your engine would not have to work so hard on the intake stroke. When the EGR valve opens and some exhaust gases are admitted back into the intake air stream this high vacuum will be re- duced somewhat. The engine will not have to work as hard on its intake stroke.

ECM controlled vacuum turns EGR on.

Exhaust gases are inert. Oxygen used in the original combustion process is gone. EGR will dilute the new air charge. In- side the combustion chamber and on the power stroke, ignition will be slightly slower producing a longer cleaner fuel burn. Slower burn will reduce exhaust temperatures and reduce oxides of nitro- gen or NOx ... that is why we don't have 11/1 compression anymore. If your eyes burn in the shop because of a particular vehicle NOx is probably the reason.

Page 52: 61689121 Automotive Engine Electronics

EGR Diagnosis

Does the EGR valve work? Take a hand held vacuum gun and hook it up to the vacuum fitting. When you apply vacuum the engine should falter or even die. This EGR valve is working. If you pull a vacuum and nothing happens then you have found the problem.

I have heard of cases where technicians have found ball bearings and other things in EGR vacuum control lines to cut off vacuum to the EGR valve. This will create a driveability problem including hesitation, shaking and surging. When the vacuum line starts to harden up vac- uum will slip around the block activating the EGR. Therefore, the EGR valve will end up being on at times when it really ought to be off. Remember, the EGR is off at WOT; so for all the performance people why let it bother you anyway?

There are three types of EGR valves: positive back pressure, negative back pressure and ported. They all do the same thing with respect to permitting exhaust gases back into the intake as necessary. You can refer to the pictures if you are interested in the particular workings. It is very important that if you do change an EGR that you install the same type as you find on the vehicle. You will have a problem if you install the wrong type.

When the ECM turns on the solenoid, vac- uum is applied to both EGR and vacuum diagnostic switch.

+ SOURCE V r n M flc 12V

ECM

1.1.11 EM

EM SOLTNOlD /1 - -

DWOSTW:

1 MCH EGR VACU)M - DIAGNOSTIC mCH

O R N

Page 53: 61689121 Automotive Engine Electronics

EGR OFF: Engine Cold In Park or Neutral Wide Open Throttle TPS Reading Low

In order for the ECM to be sure that the EGR is working when it is supposed to be two types of diagnostic sensors are used. The EGR vacuum diagnostic switch is closed when vacuum is applied to the EGR valve. Note that vacuum first goes through the controlling vacuum valve when the ECM turns the valve on. Vac- uum passing through the valve is applied to both the EGR and the vacuum diag- nostic switch. If the ECM turns the sole- noid on, by grounding the control power circuit, the ECM expects to see a circuit created through the vacuum diagnostic switch. If this circuit is not completed the ECM will think that no vacuum is going to the EGR so the Check Engine or Service Engine Soon light will be turned on. If the ECM sees a circuit created by the vacuum diagnostic switch and the ECM has not turned on the EGR the Check Engine or Service Engine Soon light will again be turned on.

Also used to keep the EGR system monitored is a heat sensing switch which is used on certain engines. This is a normally open, thermally controlled switch, which will close when it reaches about 600.F. This switch closes and cre- ates a signal for the ECM to know EGR is working. These switches have had a high failure rate because the sensor is fragile. The switch is attached to the end of the connecting wire. Then the switch

EGR DENTFEATION

D I A 16648727

ASSEMBLY RAHl COOE

D I A

6 3 1 4

BULT

PART NUI.BER

06641727

P

[P I -- P 0 8 M BAa( FfEGSUR [N] - - MEGb,rmE BACX PAEffiURE [ 1 - - W - P O A l E D V A L V E

TEMPERATURE

was encased in a ceramic centered, metal jacketed body which in turn would thread into the outside of the EGR flow passage housing. The sensor does not actually touch the exhaust. It gets heat from the housing where the exhaust gases pass through on their way back to the intake manifold. If the switch breaks loose in- side the ceramic an open circuit will develop and the the Check Engine or Service Engine Soon light will be turned on. Under these conditions carefully inspect the temperature switch. Be care- ful, it is very fragile.

Page 54: 61689121 Automotive Engine Electronics

Engine idle speed is determined by the ECM and is controlled by the Idle Air Control valve. When the engine is cold idle speed is increased similar to a stan- dard carburetor choke. As the engine warms, idle speed will be reduced.

Inside the throttle body an idle air con- trol passageway permits air to move past the "pintle" which is moved in and out by the small motor of the IAC. There are two windings used to move the pintle, one winding extends the pintle and the other winding retracts the pintle. Air passing the pintle maintains idle rpm.

Idle speed is maintained by the IAC which is mounted in the throttle body assembly and is controlled by the ECM.

When the car is at cruising speed the IAC will totally close off the air passage allow- ing the throttle body to totally control air entering the engine.

When the engine is turned off the IAC motor will seat the pintle and then retract the pintle about 213 so that the engine will quickly start when the engine is next cranked.

IAC operation will maintain engine speed during warm or cold operation for optimal performance.

Page 55: 61689121 Automotive Engine Electronics

BUFFER CIRCUIT

VEHICLE SPEED SENSOR

In order for the ECM to maintain proper control of engine and transmission func- tions,vehicle speed is needed as an input.

This important reading is provided by either an optical sensor mounted in the speedometer head or a Permanent Magnet or PM generator mounted in the transmission. Readings provided by ei- ther sensor will be in the form of a square wave voltage reading. An increase in speed will produce an increase in the number of waveforms received over a given period of time. The ECM will take the square wave frequency and compare it with the ECM internal clock. This frequency comparison will be used to determine vehicle speed.

It is important that VSS wires leading to the ECM not accidentally be placed near other high voltage wires. Such a condi- tion could induce a voltage signal into the VSS wire which would affect signal inter- pretation by the ECM.

With the optical type sensor, any foreign material either on the rotating vane on the speedometer cable or on the optical sensor will affect the VSS signal. If there is a problem with this sensor be sure to check the rotatingvane. There have been recorded cases of grease affecting the sensor. Grease can be forced onto the vane and sensor by pressure speedome- ter greasing techniques. These unaccept- able techniques include both grease nipple fittings which can be attached to the cable end by the transmission for quick grease application and by someone greasing the cable by using shop air presssure to simply blow grease up the cable using some cup grease and a rag over the end of their air nozzle. D o not use these techniques, they will produce major problems.

PM GENERATOR

WIRING HARNESS CONNECTOR

Page 56: 61689121 Automotive Engine Electronics

CHARCOAL CANISTER

VACUUM WMlFCC / SOLENOID

ECM WMROLLED AJRUV&V€ . PORlED VAalUM /!!7 -

N E L T M K V ~ R cowEcnol '4 UNE

Evaporative Emission Control System (EECS) is used on all vehicles to reduce fuel vapors which would escape into the atmosphere. A canister containing acti- vated carbon (charcoal) will soak up fuel vapors when the vehicle is not running. When the vehicle is running, captured vapors will be purged from the canister by using engine vacuum to pull these vapors into the engine so that they can be con- sumed during the combustion process.

Canister purge will start after the engine has warmed up and gone into closed loop operation and when TPS throttle signal to the ECM indicates that the throttle is off idle.

The ECM controls a vacuum source which will be applied to the canister purge valve. With vacuum applied a diaphragm valve will be lifted. Lifting the valve will cause airflow through the can- ister because of the applied ported vac- uum or pcv connection. A filter on the bottom of the canister will allow air to enter the canister.

If the canister purge valve leaks then the engine will run very rich until the canister is finally empty of fuel vapors. This con- dition will be aggravated by heat soak conditions which would fill the canister. To check the canister there are two checks. First, hook a short length of tubing or hose to the lower port and try to blow through it, there should be no flow unless the canister has a small purge hole which will only permit a small amount of air flow. Next, apply a hand held vauc- cum pump and apply 15" Hg. for 20 sec- onds. If the diaphragm does not hold this amount of vacuum then replace canister.

Visually inspect the canister for evidence of cracks or other damage which will require replacement. If fuel leaks from the canister it will have to be replaced. The filter on the bottom of the canister is a replaceable item. If it is dirty or has been damaged replace it.

Page 57: 61689121 Automotive Engine Electronics

SECTION 2 DRIVEABILITY DIAGNOSIS

In this section a "systems" approach will be used to determine which system is causing the driveability problem. Analysis by "systems" will allow you to determine if: fuel, ignition, mechanical or electronic systems need attention.

In Section 1 the general building blocks of today's electronically controlled automo- bile have been addressed. In Section 2 these building blocks will be incorporated into systems so that a procedure or method can be followed to logically determine where you will need to concentrate your investigation.

If the "Service Engine Soon" light, which used to be called the "Check Engine" light, is on then pull the ECM codes. Jumper A to B of the ALCL and read the flashes for code determination. Use these codes to help you in diagnosis. These procedures are discussed in detail in this section. Page D32 lists codes. No vehicle will have all of these code possibilities.

If you use a scanner refer to the scan related material included in this manual to speed your diagnosis. Be careful that you read your scanner properly. Scanner manufac- turers include an instruction manual with their equipment. If you have not read this information then you need to spend some time with your scanner manual.

CHAT the Computer Harness Adaptive Tester is included in Section 2 so that you will be familiar with its operation. CHAT represents a natural extension of diagnostic equipment, incorporating accepted factory service methods, used for analysis of automotive engine electronics. CHAT can be used by itself or you can use a scanner with CHAT installed. CHATdoes not affect the ECM "mode of operation" like the scanner does.

Voltage is the "language" of the ECM. CHAT was designed with one specific objective: to provide you with easy access to each wire of the ECM. CHAT allows extremely quick voltage and continuity checks for all ECM wires and circuits.

You need to know and understand what these voltage readings represent in order to service today's cars and trucks. That is precisely why you are reading this book! So you will have a better understanding of automotive engine electronics. You need to be able to interpret and understand the "language" of these electronic compo- nents in order to be successful in what you are doing. Define success as the increase in the size of your paycheck after you understand how all of these electronic items make the engine work.

Page 58: 61689121 Automotive Engine Electronics

Troubleshooting requires that you be able to determine what is causing the problem with your car. Whether you have been in the automotive trade for many years or only a few years it is still necessary to approach a problem auto- mobile in a logical and organized man- ner.

Somewhere you have probably looked at some book that has told you about how to approach a problem car. However, I really doubt that the author of that book asked your problem car if it could read in order to cooperate with his book!

Let's get serious. There are potentially all sorts of ways to attack this problem of driveability,which we will define as any sort of problem relating to the way the engine and powertrain work, but lets look at a method which will hopefully be very logical to you. I have been diagnos- ing and fixing cars for many years and there are several things which must work as Systems or else your car will not run properly.

My personal background strong point is in engines so I am approaching this prob- lem of driveability from that of an engine mechanic or technician. If you happen to be a transmission expert then you may very well look at driveability from a totally different viewpoint ... such as the

engine being a boat anchor attached to your "perfectly good" transmission. However, I look at it from the other end, andwhat is bolted to the backof theblock is somebody else's problem. I might say you have a transmission problem and even be able to pull one apart but I make it a point to let the transmission guy be the "expert" on the inner workings of transmissions. I am the engine expert and I do not fix transmissions, or at least I would not admit to it if I did. There are many people in the automotive repair trade which claim to know everything there is to know about a car .... watch out for these guys. If you can, try to specialize in just a few areas so you can be the best in several areas. Learning new things is great but, the more you learn in one week, the smaller your pay check will be on Friday!

In order to be an engine expert I have to have a quick and logical way of approach- ing engine related problems. Always use this method and you will never have to worry about second guessing yourself. The objective is to fix it right the first time which means that my first objective is to determine which system the problem is in. Then I will worry about what is specifi- cally causing the problem. However, the first thing I always do is determine just which system is creating the problem.

Page 59: 61689121 Automotive Engine Electronics

A SYSTEMS APPROACH: FROM AN

ENGINE SPECIALIST'S POINT OF VIEW.

There are four systems which we need to use in our evaluation and diagnosis:l) FUEL, 2) IGNITION, 3) MECHANI- CAL and 4) ELECTRONIC. These areas do overlap, but if we organize our thinking we will be able to clearly define where one area is so that we can logically deal with the problem.

FUEL SYSTEM. Consists of electric in tank fuel pump, supply lines, fuel filter, injector(s), pressure regulator and return line for all fuel injection systems.

IGNITION SYSTEM. Consists of pickup sensor and the device it is sensing, ECM timing circuitry, HE1 control mod- ule, ignition coil(s), and connective wir- ing.

MECHANICAL SYSTEM. Heads, block, intake, exhaust, nuts, bolts, belts, oil pump, camshaft, crankshaft, water pump,timing chain or belt, and similar so called "hard" parts.

ELECTRONIC SYSTEM. ECM, en- gine wiring harness, sensors, output de- vice and ALCL.

PORT FUEL INJECTION

FUEL SYSTEM

f-- - FUEL R M UNE II, " UNE

FUEL PRESSURE REGULATOR ki

1- FUEL PRESSURE

RETAINING CUP

w INJECTOR

Let's look at how a systems approach can get us through the diagnosis quickly and accurately. Always start at the fuel sys- tem. If you do not have any fuel the car will not run. If by chance you have bad or contaminated fuel the car will run poorly at best. Our concern is fuel pressure, fuel delivered by the injector, and ECM injector on time.

Page 60: 61689121 Automotive Engine Electronics

FUEL TANK

I FUEL PUMP I

I FUEL FILTER ( 1 I

I I I

I PRESSURE

REGULATOR

ENGINE E FUEL FLOW SYSTEM DIAGRAM

Fuel rail pressure should be within specifications.

Supply the fuel pump with 12 volts through the fuel pump test lead located in the engine compartment or

35 to 42 PSI

Verify ECM ground driver with engine running or cranking to pulse test light.

12 volt will be applied with ignition on. Special 6 volt test lights are available which plug directly into harness. Regular 12 volt

test light will work as shown below.

- - ' 1 (y--T,l \ ' +I2 VOLT I I I \ -->

I '-

\ / ' I I

- ---/ \' I

<'

ECM

12 VOLT

Page 61: 61689121 Automotive Engine Electronics

Spark plug wires should have a resistance of about 5,000 ohms per foot length. 2 foot long x 5,000 = 10,000 ohms

With the ignition system the first thing to ask is there spark coming out of the plug wire? Of course you could remove a plug wire, then take a small screwdriver, stick it in, hang near a good ground and crank the engine to see if a spark jumps. This is a "quick and dirty" method, but it is not 100% accurate. If you do have a coil problem then you will not have subjected the coil to a satisfactory test. Use a spark plug adaptive tester such as the ST 125 or simply remove the ground electrode from an old spark plug so that the spark will have to work harder to jump the gap. Be sure to attach a good ground to the body of your test plug.

IF YOU WANT TO FIRE TWO SPARK PLUGS AT THE SAME

TIME, HERE IS HOW IT'S DONE.

G n n - 9 B t - - - +

L!"Cnnnnq B t - - 9 +

CAUTION: Distributorless ignitions systems have extremely powerful coils. If one or both wires are open or disconnected, you can receive a much more powerful shock than on conventional HE1 systems.

Page 62: 61689121 Automotive Engine Electronics

I NO RECHECKS I ' t "Y If this light blinks when the engine is being cranked, the ECM is receiving a reference signal from the ignition system.

.*. .

Mechanical systems benefit from a good visual inspection. In fact the first test you need to perform is a good visual inspec- tion. When you jump to conclusions without carefully checking things out you always end up making an error in diagno- sis. There are 15,000 parts in the average automobile. Your probability for a , wrong diagnosis is high so take time to carefully inspect each vehicle before you make a final diagnosis.

Electronic system consists of the ECM, wiring harness, input sensors and output devices. This is the last system to look at simply because it is the most difficult to deal with. If you have a "check engine" or "service engine soon" light then immedi- ately deal with it. However, be sure and ask yourself "why" did this problem oc- cur. If you have a vehicle which repeat- edly blows up the same thing then you have been missing something.

Page 63: 61689121 Automotive Engine Electronics

ECM SENSOR INPUTS ECM CONTROLLED OUTPUTS

Q Electronic Control Module E - 4 9 "

0 0 q z ?

ROM

CLOCK I

RAM PROM

Page 64: 61689121 Automotive Engine Electronics

ANALOG SIGNAL

VOLTAGE

NEUTRAL

- VOLTAGE

SIGNAL WAVELENGTH

DIGITAL SIGNAL - O N TIME

OFF

CLOCK SIGNAL

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

Sensor signals are converted from analog to digital so that the ECM can process input information.

Digital signals are converted into binary words which are processed by the ECM. On page D8 is a chart which illustrates how the ECM can count up to 255, which means that all 8 switches are in the on position. If the ECM adds 1 more to 255 all the switches will be turned off, repre- senting "0".

-

Analog signals can be continuously vari- able in both voltage and frequency. Digital signals are variable but not con- tinuously. Digital signals can be off or on, yes or no, or high and low. This would be called a digital binary signal. One level is a positive voltage, the other is novoltage. As you can see in the above picture a digital binary signal produces a "square wave".

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D 8 Automotive computers do everything according to a detailed list of instructions which is called the program. Automotive programs take into effect all possible combinations of sensor input so that the best degree of driveability will result. For example, cutting off the a/c compressor when the TPS indicates wide open throttle, so maximum acceleration will be possible.

A microprocessor functions as the "brain" of the computer, since it does all the necessary calculations. All other parts of the computer support the micro- processor.

Since the microprocessor cannot store information it has specialized memories. ROMs, RAMs and PROMs are the memories of the automotive computer. Read Only Memories or ROMs are used for permanent storage of information, which is programmed in when the ROM is built. Random Access Memories or RAMs act as the file cabinet because temporary information can be stored and retrieved from there such as current sensor input values used by the micropro- cessor. Most RAMs are of the "non- volatile" design and will lose their stored information if power is removed. Pro- grammable Read Only Memory or PROM can be removed from the ECM. PROMs are used to provide the ECM with specific design and operating char- acteristics for each car model, even though the same ECM type may be used in several car lines.

ECM uses an "8 Bit" microprocessor. 8 segments make up each "word".

255 is the largest number which can be recorded with an 8 Bit chip.

Page 66: 61689121 Automotive Engine Electronics

-

AIR DIVERT AIR DIVERT SOLENOID SILENCER

CHECK VALVE

- - FUSE & HOLDER :kESSURE

SWITCH

Page 67: 61689121 Automotive Engine Electronics

Scanners read what information is sent along the serial data stream. Scanners are extremely helpful, if you know what the heck they do and how they interface with the ECM. Scanners do not provide all the information. They do however, provide some very useful information and they also provide some information which on the surface may seem correct but can cause driveability problems. It is extremely important to understand just how far a scanner can take you concern- ing diagnosis.

Were you aware that the computer is like a 4-speed transmission? You plug the scanner into the Assembly Line Commu- nication Link (ALCL) or Assembly Line Diagnostic Link (ALDL), which are the same connector called different names by the various car divisions of GM. In this manual we will use ALCL to identify this connector, however if you see ALDL be aware that it is the same device.

When you install the scanner onto the car you change the way the ECM operates. In fact the ECM has four modes of opera- tion: open, diagnostic, fuel back up, and special or ALCL mode. Most scan tools are designed to automatically switch the ECM into the special mode of operation. Because of this many technicians are not aware of the other modes. This has caused many problems, such as trying to set engine idle speed and the scanner has sped the engine up to 1200 rpm, which is

ALCL Connector Terminal Identification

F E D C B A

A - Ground Terminal B - Diagnostic Enable C - Exhaust Port Air Switching Solenoid D - Service Engine Soon Light E - Serial Data F - Torque Converter Clutch G - Fuel Pump Test Lead

Not all terminals are found on all engines.

Create a circuit on A9 in order to receive ECM Serial Data from terminal E.

,- SERIAL DATA 1 1

Page 68: 61689121 Automotive Engine Electronics

part of the ECM's programming when put into the special mode.

Unfortunately, scanners can get you into trouble. When the computer is in special mode they cannot spend all of their time taking care of engine operation. Some functions become locked in because the microprocessor does not have time to deal with them because the microproces- sor must take time out from its comput- ing function to answer your questions ... such as integrator and block learn or any other request which you enter in your scanner.

Special mode is the only mode where you can get fairly reliable information, but you need to keep this in mind, fairly accurate not totally accurate.

Scanners can also shift the ECM into the fuel back up mode where the engine will run on the calpac. Or, the engine can be put into open mode, where it normally operates. If the engine is in open mode you probably will not get accurate infor- mation. If you do get good information that'sgreat. But if you want TPS and with your foot flat on the floor your reading is .45 instead of 4.5 then I would not believe your scanner.

The final mode of operation is the diag- nostic mode where the scanner could ground the diagnostic terminal in order to flash the service engine soon light in order to use the light for code retrieval or check EST operation. Some scanners will not do this because of electrical cir- cuit problems with the external power source from the lighter.

Scanners apply specific resistances across the A and B terminals in order to change ECM modes of operation. Normal operating mode is called 20,000 ohm which is an open circuit with no connection.

DIAGNOSTICS I A9

SCANNER I I ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - -I

MODE A-B RESISTANCE A9 VOLTAGE

Open 20,000 ohm 5.0 volts ALCL 10,000 ohm 2.5 volts Fuel Backup 3,900 ohm 1.4 volts Diagnostic 0 ohm 0 volts

Page 69: 61689121 Automotive Engine Electronics

Integrator and Block Learn are two read- ings which tell you how much fuel the ECM is providing to the engine. These values can be read with the scan tool and are extremely important for you to un- derstand.

As you are aware, the ECM will inject fuel into the engine based upon sensor inputs. However, reference, throttle position and coolant sensors are the most significant inputs with the other sensors used to fine-tune fuel delivery.

In the section which discussed the micro- processor it was covered that 255 was the highest number which could be recorded with an "8 bit" computer chip. If you count the possibilities of 0 to 255 then 128 would be the mid point.

128 is the mid point for both integrator and block learn. If the engine needs additional fuel then a higher number will be registered to indicate an increase in injector on time. If the engine is rich then the numbers will be less than 128.

Now that we have covered the basic prin- ciple of integrator and block learn, which are two different values, let's explore them in greater detail. Imagine that you are taking a four year old kid to the toy store. Whenever something new pops up the kid is off and you sort of tag along.

Integrator and Block Learn will both read 128 when the car is not in closed loop operation.

m u 0 1 SCANNER

Integrator and block learn work the same way. Integrator is the first value to move and after a while block learn will move over to that point. However, now that the airlfuel ratio has been corrected to the right value (14.7 to 1) our integrator is ready to take off in either direction again as needed. For example with a small air leak downstream from the mass airflow sensor the ECM will think it's running lean because of the air which has not been accounted for, thus it will command a longer on time. Since this is a perma- nent condition, the block learn might be 150, indicating extra injector on time, with the integrator value at 128. If the air leak were greater then both values would be permanently over 128.

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Before the engine goes into closed loop operation both integrator and block learn values will be fixed at 128. When the ECM gets a strong acceleration com- mand both values will again be locked in at 128. Injector on time of 128 does not mean that the injector is on 112 the time the engine is running. It means that the injector is held open 112 the amount of time which could possibly be allowed by the program in the PROM. There are limits to injector on time. On passenger cars 90 to 150 could be the range. On per- formance vehicles the maximum on time could increase to around 200.

An engine with a restricted intake or a restricted exhaust would run rich be- cause it could not properly breathe. Thus the ECM would reduce fuel delivery in order to maintain 14.7 to 1. However, during full throttle bursts or engine warm-up a very rich condition would result because the full fuel charge would be delivered to the engine.

If you have a scanner then make a note of integrator and block learn values with the engine idling in closed loop. Induce a small vacuum leak and note what hap- pens. Partially restrict the air intake and note your readings. If you have a scanner, then integrator and block learn are two values which you need to closely check on each car. Remember, if the car did not have a problem you would not be doing this! Learn about these values, they apply to all EFI and PFI vehicles. Inte- grator and block learn values are two of the most helpful values you can get from the ECM on your scanner.

More fuel is delivered due to a lean condition such as a restricted fuel filter.

( 128 150 I SCANNER

Less fuel is delivered due to a rich condition such as a restricted air filter.

1128 90 /

SCANNER

More fuel is delivered due to a lean condition such as an air leak.

-

INT BLOCK

SCANNER I

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Scanners can get you into trouble and you need to be aware of their limitations. Scanners receive all of their information from the serial data transmitted from the ECM. This information represents a "snapshot" of what the ECM has stored in the RAM. Therefore, there are certain readings which will appear to be correct but are not in fact accurate enough for your diagnosis.

A very good example of this is TPS, and you should perform this experiment so that you will know exactly what limita- tions you are dealing with for scanners. If you access the scanner reading of TPS and compare it at the same time you have installed a digital multimeter on the TPS signal wire you will notice the difference clearly. Scanners will give you a TPS reading but this is not sufficiently accu- rate to set baseline TPS voltage readings. Set the DMM to the 2 volt dc scale and note the real ECM signal input. Com- pare this to your scanner. Move the TPS arm through a small arc and you will see that the sensor provides variances in thousands of a volt (.001). Scanners will vary but their variance is really only reli- able to the first decimal place (.I). This degree of accuracy can cause the baseline setting where .45 volt (3.8 l), + or - .075 volt can really get you into trouble.

Perform this little check and you will see how easy the scanner can get you into

trouble. Technicians who have used the scanner to set TPS on CCC carburetor vehicles and have gotten away with it will cause driveability problems with fuel in- jection. Remember that canister purge and TCC are ECM outputs which look at the TPS signal.

When you install the scanner in the diag- nostic mode you will not always get the proper diagnostic codes. Always per- form a Diagnostic Circuit Check and then use your scanner to rough out the problem area affecting your subject ve- hicle.

If you use the scanner in any mode other than the ALCL 10K mode you need to be extremely cautious of any reading you do get. If the coolant temperature is locked in at one value or the car stays in open loop, according to the scanner ... switch to the ALCL mode and verify your reading. There is no sense trying to fix something which isn't broke.

Scan tools allow for a quick check of sensors and switches. Serial data only updates every 1.25 seconds and vibration induced intermittents will not necessarily show up on the scanner. Remember that the scanner interprets the sensor input wire. However the sensor functions as part of a circuit and thus any problem in the circuit will have some type of effect upon the sensor reading even if the component is perfectly good.

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Amps,volts and ohms are the language of today's automotive electronics. You need to know how to measure each of these values in order to service these vehicles. If you do not feel comfortable with amps, volts and ohms then review the sections of this manual which deal with these subjects. It is very important that you fully understand how these elec- trical characteristics inter-relate with each other.

Volts represent electrical pressure. Measure volts at any point in the circuit. Amps represent how much current flows through a circuit, sort of like how wide is a river for example. Ohms act as the resistance to flow, the more resistance the less flow.

Ohm's law is the equation used to express the relationship between these elements E=IxR. Volts = amps x resistance. Perform the diagnostic checks on each circuit so you will know just what is hap- pening.

Continuity checking will tell you that your wires go where they are supposed to. If you have a short it would be like trying to wash your car with a hole in the hose ... the water would not get to the nozzle. With a short the current is flow- ing somewhere it is not supposed to. Shorts generally occur to ground and tend to blow fuses and burn up wires.

Occasionally you will find a short to power where a wire will have come in contact with an unwanted source of power. This can come from defective insulation, or internal component failure so that current can pass through a com- ponent in a way it is not supposed to, or a physical connection existing between the two circuits in question. Knowing how to check continuity will allow you to be sure that your wires go where they are supposed to and only where they are supposed to.

Voltage readings of sensors is made by installing jumper wires and attaching DMM.

DIGITAL MULTlMEl 'ER

TPS VOLTAGE CHECK

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Resistance measurments are made across the component.

Continuity checks are made with the circuit isolated.

200 OHM 0 Voltage checks are made when the circuit is operational.

Amperage checks are made by allowing all the current to flow through the meter.

20m DCA

Page 74: 61689121 Automotive Engine Electronics

Schematic diagram of circuit.

R+ 12v

RELAY 7

E C M

L

- - -

- -

Continuity test of individual wire in harness. Disconnect ECM before testing.

SENSORS

Continuity test of control wire to relay.

0 200 OHM

10

B+ 12V

RE LAY .-. - : $ - - -

COOLING FAN $@= -

- -

Voltage test for each ECM wire is performed with with ignition on and idling in closed loop

Page 75: 61689121 Automotive Engine Electronics

High impedance digital multimeters are necessary to perform checks of the auto- motive electronic system. Throughout this manual you have seen it and now is the time to explain why you must use this type of meter.

Remember the discussion of magnetism and how current flowing in a wire created a magnetic field? That technology is used in the older "swing needle" type of meter. Consequently, it takes a lot of current flow in order to make this meter work. Additional current flow can cause you problems because this type of meter can damage the sensitive electronic circuits of the ECM.

The ECM has circuits which are primar- ily designed to handle 112 amp of current flow. There are "protected" ECM cir- cuits which have greater capacity, such as the fuel injector drivers, but these are different than standard sensor circuits.

By now you realize that a sensor signal can involve only a small amount of actual current because the voltage present will act as the information carrier. Older swing needle meters require so much current flow that they could totally con- sume some signals. High impedance digital multimeters require so little cur- rent that it is difficult to measure how much they would affect a circuit, out of the laboratory environment.

Pictures included in this text show how the meter is supposed to be used. Refer to the pictures if you have questions about meter installation. However, it seems that one of the most difficult prob- lems is the reading of the meter itself. If you have experienced difficulty with re- ally understanding all of the symbols and settings of your meter then you will need to do a little homework. You may not have done homework in years but this can be both fun and interesting!

Take your digital multimeter and hook it up to some sensors which have variable outputs and take the time to understand exactly what you are doing. For instance, I removed the 3 wire connector to a TPS and set my DMM to the 20 K scale (K is 1,000 so 20 K is 20,000 ohm, the only 20K scale is for ohms on your meter). I in- serted one probe into the center terminal and one lead into an end terminal. My meter said 1.8K. I moved the probe from the end terminal to the other end termi- nal and the meter read 5.15 K; this was correct. I moved the TPS throttle arm by moving the throttle valve and my meter resistance dropped to 1.8K, indicating wide open throttle. How did I know that I had originally installed the meter back- wards? Ohm's Law, that's how. With high resistance the ECM, off the center wire, will read low voltage. So when properly installed, high resistance will

Page 76: 61689121 Automotive Engine Electronics

fall to low resistance and so the ECM will see an increase in voltage signal.

Install three jumper wires to the TPS, or install the CHAT unit and perform this test with the meter set to 20 DCV and turn on the ignition. Move the TPS through its' operating range. TPS should vary smoothly. Just for the heck of it, if you have a scanner hook it up and com- pare its' reading to your DMM, you will be shocked at how far off the scanner is, especially with the DMM on the 2 DCV scale. Remember that most of your driv- ing is done with TPS below 2 DCV.

Now let's try turning our attention to the oxygen sensor. Insert a jumper wire or simply hook into the CHAT unit sensor signal. Again, the DMM should be on the 2 DCV scale and you can see exactly what voltage you are generating. This is agood hookup to inspect for rich or lean run conditions which would include canister purge and vacuum leak diagnosis. Air leaks will pull in propane if you use an enrichment tool. The meter will immedi- ately pick up any change in sensor output. Remember to never try the ohm test across an oxygen sensor, it is a voltage generator and could be damaged perma- nently because an ohmmeter placed energy into a circuit to make resistance checks.

If you have problems reading the meter, take it home and play with it. Take along a couple of sensors and do some experi-

mentation until you really feel comfort- able with your meter. Anyone who had made it this far reading this book needs to know everything about that meter. It is the device which will tell you if a problem exists. Have you ever seen the flashing lights of a police car behind you? Well, if you have then you know that he's trying to tell you something!

If you do not fully understand how that meter works you may have a problem getting the message! Be sure to know all there is to know about your meter. If your meter has a diode check, then go by your local Radio Shack store and pick up a diode assortment and try them. And, if you really start getting into this whole thing, break down and purchase one of their "200 in 1" experiment kits when it is on sale. You will be able to build all sorts of things. Take that DMM and work it through some of these circuits. Figure out why diodes are in certain places. Figure out why capacitors are placed as they are in your circuits. A couple of hours, when you can, this electronic stuff will really make a lot of sense which will help you out on the job. Remember, we want to do it right the first time!

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Now that you have mastered the DMM you are ready to get the information out of the car. By now you know that the scanner does not have all the answers, only some of them. Now we need to get to the bottom of things and that is where the DMM becomes your top tool.

Accessing all of the circuits is tough, it does require work and it requires circuit understanding. If you find that you need a particular type of connector then you will need to make up some test jumper connectors. These are available from your friendly tool truck man and will do a good job. However if you find that you need a specific type of connector which has not made it into his selection yet, then you need to make a trip to the junk yard. For a couple of bucks you can get all sorts of connectors which will fit the specific types of vehicles which you work on.

After you have the connectors then they need to be prepared for service. Termi- nal ends need to be fitted to the ends of the connectors so that you can quickly install them to make your circuits opera- tional. If you are using the standard "weatherpack" type connectors then these can be had from any GM dealer under part number 12014836 and 12014837 for the male and female termi- nals.

If you are using the very small connectors then a paper clip of the proper diameter

and cut to length will make a good con- nection. Remember to crimp and solder with rosin core solder to ensure that a good connection exists, just like with every electrical repair which you will make on the ECM wiring harness. Do not use crimp connectors! Or, you will have intermittents which will begin the day the car leaves your shop!

After you have your jumper cables and wires you will have access to the wiring harness in order to make necessary checks with the DMM. Of course, you will need to know just what circuits you are checking and what types of readings you are getting. These readings would then be compared with what you person- ally would anticipate them to be and you would also reference the expected read- ings listed in the shop manual or in the reference section of this text.

Keep in mind that no reference is 100% right. That is why you need to have an idea about the reading which you are getting. Is the reading which you are getting from your DMM what you per- sonally think should be coming out of that sensor? When you understandECM and wiring harness circuitry then you will feel comfortable making this type of decision. Of course, do not overlook performing the same test on a known good car, this is a good way to verify test results.

Page 78: 61689121 Automotive Engine Electronics

CHAT, the patented Computer Harness Adaptive Tester, is the most significant new diagnostic test tool for GM cars and trucks. CHAT has been designed and built for the tune-up and electrical tech- nician servicing highly complex engine control systems. Because of its interface features, CHAT is the most sophisticated service tool available to professional technicians.

In recent years diagnostic computer in- terface systems have been developed to help with the service of complex automo- tive engine electronic systems. These devices can cost $18,000 and use an ECM interface terminal to provide vehicle data for analysis.

CHAT provides a way to access each wire, sensor, solenoid, relay, and control used for all ECM engine functions. CHAT uses the exact same Packard Electric connectors which are in the original equipment wiring harness.

All CHAT tests are performed with a digital multimeter and this data need only be compared with available diagnos- tic and ECM voltage charts so that neces- sary decisions can be made in order to fii the vehicle. CHAT costs about the same as a scan tool.

In order to fix the car you have to deter- mine exactly what is wrong with it in the first place. Finding out what is wrong can be a difficult task ... especially if you do not have any idea about what is causing the problem. You must understand how the ECM system is designed to work if you want to fix it.

There are logical service procedures for the electronic system. These procedures take into account the operational para- meters and provide you with a logical sequence to approach driveability prob- lems. In fact, after you become comfort- able with the right way to perform diag- noses and you become confident with the fact that it is possible to fix the electronic system you will probably become very proficient with this system.

If you use CHAT you will be performing voltage, continuity and short testing. These are the same tests you would be performing without CHAT only now these tests are easy to do.

As you become more confident with ECM operation you will be turning the corner into the newest area of automo- tive technology. Very few technicians are competent in this area. CHAT will help you achieve success with difficult drivea- bility problems by making necessary di- agnostic checks quick and easy to per- form.

Page 79: 61689121 Automotive Engine Electronics

Performing voltage, continuity and short testing will have to be done if anything other than a simple sensor failure occurs. Perform a diagnostic circuit check and see what the ECM tells you. If you have a code then you need to deal with the code. Always start at the lowest code and work up, unless you have a 50 series code and then go immediately to that. To get the codes simply jumper terminal A to B in the ALCL and watch the service en- gine soon light. It will blink code 12 three times, followed by any recorded codes, and repeat the code 12 again. Code 12 will be one flash followed by a pause and then two flashes of the light. Code 34 would be three flashes, a pause, and four flashes, for example. See the reference section of this book for code identifica- tion.

If the sensor checks out then you need to go into the wiring. You will need to drop the ECM from its mounting and see just what voltage is getting to the ECM on the appropriate circuit. After you remove the ECM you will need to remove the retainer comb in order to gain access to the back of the wire entering the ECM header connector. You can now use the exposed wire end in order to perform ECM header connector voltage testing or use the DMM and go from the appro- priate terminal on the connector back to the sensor connector to verify wire conti- nuity.

If all of this activity up under the dash sounds tough; well it is, especially when you perform wiring continuity checks. However, if you have CHAT then these tests are much easier. If you have the CHAT unit simply remove the header connectors from the ECM which you do not need to remove. Leave the header connector wiring retainer combs in place and plug the header connectors into the CHAT junction head. Install the jumper harness from the junction head to the ECM and you have completed CHAT installation.

To perform voltage checks from the CHAT pinout first verify the ground ter- minal using your DMM on the 200 ohm scale. If this ground checks then insert the black probe into the dedicated ground and simply select the circuits you need to check. Refer to the reference section of this manual as necessary. If the ground does not check out, attach the DMM black lead to a good ground and perform the tests. If your results do not match the reference values, inspect the engine grounds. The dedicated CHAT ground is tied to one of the engine grounds which use terminal A-12.

Refer to the diagrams about installation and voltage testing with the CHAT tool.

Page 80: 61689121 Automotive Engine Electronics

D 23 Voltage tests are

CHAT used in the performed like this. performance of voltage and continuity tests. b l u U M m

Continuity tests are performed like this after removing ECM

Page 81: 61689121 Automotive Engine Electronics

To perform continuity checks, first re- move the two jumpers from the CHAT junction head to the ECM. You do not want your results influenced by the ECM. Insert one DMM probe into the appro- priate CHAT pin out terminal and touch the other probe to the wire in the connec- tor which would attach to the sensor or output.

With CHAT continuity checks can be performed very easily. Without CHAT continuity checks must be made with one ohmmeter probe up under the dash stuck in the back of the header connector while you are out under the hood with the other probe. Without CHAT this vital test is difficult, slow, and not too reliable.

To perform a short to ground use the same setup as for continuity with the ECM jumpers removed. Simply place one probe in the suspect circuit pinout and touch the other probe to the dedi- cated ground terminal. If the DMM shows continuity on the 200 ohm scale, then you will need to trace the wire. If your meter makes an audible beep when continuity is established you can shake the harness to speed diagnosis.

Not all scanners will work with all GM cars unless the scanner has been appro- priately updated with the annual changes. You can use your DMM on any

GM vehicle with header connectors 1 which will accept CHAT.

I CHAT uses Packard Electric connectors 1 which are the same type used to build the I wiring harness. If you need to attach I CHAT into a Body Computer or BCM you will have no problems. Be sure to reference the appropriate service man- ual for readings of the 24 pin and 32 pin connectors. CHAT will also fit the newer P4 computers, simply watch which circuit you plug into so that you do not get your circuits confused.

Electrical Danger

The ignition should always be off whenever removing or reinstalling

ECM connectors.

Page 82: 61689121 Automotive Engine Electronics

G R O U N D P I N - O U T

CHAT

C H A T

0000 8 A9 A 1 D A l l A12 @ 0 0 0 GROUND 0 9 B I D E l l 6 1 2

00000000 C9 C10 C11 C12 C13 C14 C15 C16 00000000

P I N - O U T \ \

COMPUTER HARNESS ADAPTIVE TESTER

NSTALLATION AND IDENTIFICATION DIAGRAM

2 0 I N C H LONG 3 2 WIRE JUMPER CABLE 3 2 P I N

WIRLNG HARNESS C O N N E C T O R

\ 2 4 P I N

24 W I R E JUMPER CABLE WIR ING HARNESS 2 0 I N C H LONG CHAT

J U N C T I O N HEAD

TO E N G I N E

T O E N G I N E

C O N N E C T O R

CHAT is covered by U.S. Patent Number 4,690,475

CHAT is available from Diagnostic Products Company

Page 83: 61689121 Automotive Engine Electronics

VOLTAGE CHECK ALL ECM WIRES AND CIRCUITS LIKE THIS

COMPARE ACTUAL TPS VOLTAGE WITH ECM VOLTAGE IDENTIFICATION CHART OR SHOP MANUAL

IF .724 VOLT WAS YOUR ACTUAL READING OF BASE TPS ON A PORT FUEL INJECTED CAR YOU WOULD HAVE TO ADJUST THE TPS.

IF TPS REQUIRES ADJUSTMENT FOLLOW SHOP MANUAL PROCEDURE TO LOOSEN TPS ATTACHMENT SCREWS AND ROTATE SENSOR UNTIL VOLTAGE SPECIFICATION IS SET. TIGHTEN TPS ATTACHMENT SCREWS ACCORDING TO SPECIFICATION.

Page 84: 61689121 Automotive Engine Electronics

0 200 OHM

32 WlRE JUMPER CABLE \\

24 WlRE JUMPER CABLE

SHORT TO GROUND OF THE DISTRIBUTOR REFERENCE SIGNAL WILL PFIODUCE A "NO RUN" CONDITION WITH A FUEL INJECTED VEHICLE.

Perform short to ground test like this.

SHEET METAL SCRRN CALISES SHORT-TOGROLIND PRODUCING A NORUN CONDmON

Page 85: 61689121 Automotive Engine Electronics

CONTINUITY TEST SHOWS WlRE IS GOOD.

32 WIRE JUMPER CABLE

24 WlRE JUMPER CABLE

CONTINUITY TEST SHOWS WlRE IS OPEN (BAD).

32 WlRE JUMPER CABLE

24 WIRE JUMPER CABLE

"OL" READING MEANS OUT OF LIMITS

Page 86: 61689121 Automotive Engine Electronics

ADVANCED DIAGNOSTIC PROCEDURES

Use CHAT to Verify Series Circuits with an Ohmmeter.

Many circuits are connected together. Components and wiring which make up an individual series circuit, can be checked for continuity at the CHAT Pin-Out.

p 9 2: A$)pApgAgAg 82 0.l B l 05 86 07 S B B l O B l l B 1 1 20K OHU 0 0 0 0 0 0 0 0 0 0 0 0

CJ C4 C5 C6 C7 D C) ClOClI Cl l C l l h % @ 0 @ 0 0 @ ~ 0 0 @ 0 ot M DI M m M 07 m a oio o t ~ o n or, ot4 01, ota \ COMPUTER HARNESS ADAPTIVE 1

\ I MANIFOLD AIR TEMP

This is an example of how i t is possible to check sensors and wiring with CHAT.

Place one digital multimeter probe into terminal D 2 of the CHAT pin-out. Then you will be able to check all wiring and sensors by continuity testing the individual series circuits, by using CHAT.

Series circuits are formed between terminal D 2 and C10, C13, C14, and C12 in this example.

Page 87: 61689121 Automotive Engine Electronics

ADVANCED DIAGNOSTIC PROCEDURES

Use CHAT to Verify Powered Circuits.

Many circuits are connected to a source of power. Components and wiring which compose each individual series circuit, can be checked for the presence of source voltage at the CHAT Pin-Out.

Also, in this representative circuit, a functional test of the brake switch could be performed by simply pushing down on the brake pedal and observing the meter reading.

1 12.2 VOLT

GAGES FUSE IGN. 12 V.

S.E.S. LAMP BRAKE SWITCH I AUTOMATIC TRANSMISSION I - Inl 1 3 1

T - TCC SOLENOID 1 I I

FIEIDICIBIA G I ) ] ( ) OVERDRIVE LIGHT

r-l M/T

OVERDRIVE SOLENOID

CANISTER PURGE SOLENOID

A3 12.2 VOLT

DIVERT SOLENOID

I 12.2 VOLT 1 (BLACK CONN.)

A2 - PORT

I SOLENOID

note: This diagram shows both automatic and manual transmission options available for this vehicle.

Page 88: 61689121 Automotive Engine Electronics

CIRCUIT TO GROUND

POWERED CIRCUITS

CHECK FOR CONTINUITY TO GROUND

CHECK FOR CIRCUIT CONTINUITY

CHECK FOR APPLIED VOLTAGE

Systems testing can be done with CHAT in order to check and verify much of the ECM wiring and sensors with voltage and continuity test procedures.

Circuits are necessary for signals to come into and go out of the ECM. If you have a CHAT unit for GM vehicles, or a pin- out for Ford or other vehicles, this sec- tion will be of great value to you.

Take the necessary time to become famil- iar with CHAT and system testing proce- dures before you go out and attack any problem cars which come your way. Knowing how to use this tool and these procedures, will save you hours of time when trying to determine what is wrong with a so called "problem" vehicle.

Refer to page D 28 of this book, which shows a conventional continuity check of a wire using CHAT.

Now, let's use a systems approach to continuity test the same TPS system. Use of a systems approach will greatly speed your testing procedure. Refer to the wir-

A TPS sensor generally has around 7,000 ohms resistance. Go between any two of the three wires with the DMM on the 20 K (20,000 ohm) scale and you should haveacircuit. In this example the tests are between C14&lD2,C14&C13orC13&D2.

Look through the wiring diagram and repeat this procedure. You will find and be able to isolate other circuits including complex circuits with interconnected sensors, switches or devices.

Many circuits use the vehicle for ground. You can perform continuity tests to ground in order to verify these circuits.

With the ECM still disconnected, switch the DMM to the 20 DCV scale and turn on the ingition. The ECM will ground powered circuits in order to turn them on. Page D 30 illustrates that "powered" circuits will be electrically hot and system voltage should be present when checked.

Voltage and continuity systems checks can be used to verify most of the ECM circuitry and components. This is a valu- able new procedure which significantly

ing diagram as shown on D 29. speeds diagnosis. This testing procedure is simply not practical without CHAT.

Page 89: 61689121 Automotive Engine Electronics

CODE IDENTIFICATION

12 - No reference (engine not running) Thb b a check d the ECM to doid a signal and d m not indicate a

problem. It dmply meana that you have no reference.

13 - Open oxygen sensor circuit

14 - Coolant sensor signal low

15 - Coolant sensor signal high

21 - TPS signal voltage high

22 - TPS signal voltage low

23 - Manifold air temperature low

24 - Vehicle speed sensor

25 - Manifold air temperature high

31 - Wastegate electrical signal -turbocharged engines.

32 - EGR failure

33 - MAP sensor signal high

34 - MAP sensor signal low

35 - IAC problem

36 - Mass Air Flow

41 - Cylinder select error

42 - Electronic spark timing

43 - Electronic spark control

44 - Lean exhaust condition

45 - Rich exhaust condition

\ \ / / SERVICE -

ENGINE SOON

/

To perform diagnostic circuit check insert jumper between ALCL terminals A & B. Read code flashes: blink, pause, blink blink as code 12. Note additional codes. Remove ECM power by disconnecting ECM fuse for 10 seconds. Start engine and see if code returns to indicate that problem actually exists. Some codes will require that vehicle be driven in order to duplicate conditions.

46 - VATS

51 - PROM

52 - Fuel CALPAC missing

53 - Over voltage condition

54 - Low fuel pump voltage

55 - ECM

Page 90: 61689121 Automotive Engine Electronics

Open loop operation exists until the vehicle reaches operating temperature. There are three things which must occur in order for the engine to enter closed loop operation.

First, the oxygen sensor must warm up and start to produce an electrical feed- back signal to the ECM, which occurs at about 600°F. Secondly, the coolant tem- perature sensor must show about 135°F. Thirdly, a given amount of time must pass so that engine rpm will have a chance to stabilize. Thirdly, there is a time element which will vary from 10 seconds on 1985 EFI and PFI models. This time element was lengthened to 30 seconds beginning in 1986. CCC systems will require about two minutes before entering closed loop operation.

When closed loop operation is reached the ECM will maintain an air fuel ratio of 14.7 to 1 for optimal emission and econ- omy operation. When the vehicle is operating in open loop a rich condition will exist to promote engine warmup.

In closed loop operation the ECM will maintain a 14.7 to 1 air/fuel ratio.

TO ENTER CLOSED LOOP:

1. OXYGEN SENSOR SIGNAL 2. COOLANT TEMPERATURE 3. SPECIFIED TIME

Page 91: 61689121 Automotive Engine Electronics

Port fuel injectors can become clogged with a tar-like residue which will cut fuel delivery. Generally this condition results from the use of fuel which does not have sufficient detergent additives and can occur invehicles having a high heat-soak. Short trips in town can produce clogged injectors.

In order to determine if there is an injec- tor problem perform an injector balance test. Specifically, this test will determine if each injector delivers the same amount of fuel. This is accomplished by turning each injector on for a specific amount of time and recording the pressure drop on a gauge attached to the fuel rail. A suitable tool is the Kent Moore 5-34730 or equialent, which contains a pressure gauge, injector tester, and test light.

Install the fuel pressure gauge onto the fuel pressure tap. Cycle the fuel pump either by turning on the ignition and letting the pump cycle for two seconds or apply 12 volts to the fuel pump test lead. Purge air from gauge line in this process to ensure accurate reading.

Remove harness wires from injectors. Install injector tester onto first injector to be tested. Cycle fuel pump, record read- ing in kPa. Fire injector and immediately note pressure reading. Repeat proce- dure for each injector. If there is a differ- ence of 10 kPa + or - from the average

then injectors will need to be cleaned. If an injector falls outside of this range then repeat procedure. Do not fire injector more than three times or you will flood the engine and soak the spark plugs with fuel.

If all injectors check within specification, check the injectors electrically. Install the test light and be sure it cycles when the engine is cranked. It is also good policy to take your ohmmeter and check each injector. Injectors may look the same but they can have different flow rates and different resistances.

If the gauge will not hold pressure then the fuel pressure regulator is probably defective and will need to be replaced. If you have very high fuel pressure look for a restricted fuel return line. If your fuel pressure is low suspect a clogged fuel filter or other restriction on the supply side.

If an injector does not deliver sufficient fuel a lean condition will exist and preig- nition can result. A vehicle surge can occur which will typically be very noti- cible upon light acceleration after the TCC has just engaged in the range of 35 to 42 mph.

If the injectors need to be cleaned, there are special injector cleaning tools avail- able such as 5-35800 or equivalent.

Page 92: 61689121 Automotive Engine Electronics

SECTION 3 SELECTED ECM VOLTAGES AND

WIRING DIAGRAMS

Section 3 includes selected ECM circuits and voltages to assist in diagnosis.

Use on& a high impedance digital multimeter ( J 34029-A or equivalent) for all ECM tests.

For voltages in the engine run column, be sure the vehicle is idling in closed loop with no scan tools installed. You can use the "Service Engine Soon" light to indicate closed loop. JUMPER ALCL A to B; if the light blinks quick (twice a second) you are in open loop. If the light blinks slow (once per second) you are in closed loop.

Diagnostic Products has attemped to make our technical information as accurate as possible. However, with the many changes which are made in production of vehicles you should verify the voltages by being sure that the reading you get from a circuit does in fact reflect the component you are attempting to test.

Revisions to this manual and particularly to this section are planned. Your tool dealer will have copies of the revised publication when it becomes available or you can contact Diagnostic Products directly so you can receive this information as soon as it is available.

Page 93: 61689121 Automotive Engine Electronics

W 2 ECM VOLTAGE IDENTIFICATION CHART

VOLTAGE 1.8 L "J" TURBO

VOLTAGE

KEY ENG ION I R U N I CIRCUIT PIN

, I I 1 KEY 1 ENG I

N O T E IN I CIRCUIT I ON 1 RUN

1 Battery 12v l nput 1 0 1 13.4 1 Fuel Pump Relay 1 ~ 1 - -- -

Not Used A2

Not Used A3 b4 ( Not Used I I 1 12.4 1 .S 1 Wastegate I A ~

-- -

13.8 Service Engine Soon A5

13.6 Ign. -- ECM Fuse A6

5 ( Reference 11.6

6 Not Used

7 ESC Sensor Signal 9.1 9.1 TCC Control A/T

ALCL -- Serial Data

Vehicle Speed Sensor A1 0

12.2 13.8 0 0

g NotUsed 0

1 0 Park Neutral Switch :& I, 13,7

11 Not Used -

2.5 MAT, MAP Ground A1 1

0 System Ground A12

0 I Coolant Fan

1 12.2 1 13.8 1 A/C Relav Control 1 ~ 2 15

D l 2

D l 3

~ 1 4

~ 1 5

~ 1 6

1 Not Us ldle Air Control --B--Low

Notused

Not Used

Fuel lnjectors 3 & 4

NotUsed

Fuel lnjectors 1 & 2

1 Not Us ldle Air Control - -B--H~Q~

12.2

12.2

1 Not Us

13.8

13.8

ldle Air Control --A--High

ldle Air Control --A--Low I Not Us

Not Used

P/S Pressure Switch

Crank Signal

Coolant Temperature

M A P - s ~ ~ ~ ~

MAT Signal

.45 TPS Sensor Signal C13

4.9 TPS 5v Reference C14 - -

Not Used 1 ~ 1 5

NOTES & SPECIAL INFORMATION VOLTAGE TESTING REQUIREMENTS:

[ I ] Fuel pump relay will read 12v tor 2 seconds when lgnttion is M c h e d on. (21 Vonage reading varier. [3] Varies trom .8 w n to battery w n depending upon driK wheel posttion. [4] Varies with ternparalure. (51 Engine running witage will be high or low depending U A/C k on or off.

1) This chart is for use with a digital multimeter. 2) Engine must be at operating temperature. 3) ldle engine in "Closed Loop" for ENG RUN voltages. 4) Diagnostic test terminal in ALCL not grounded. 5) No "Scan" tools installed. 6) "Key On' readings represent known good battery.

[8] Note voltage change when s h ~ e d Into gear for autoihalIitransrnosaon. [TJ Hdl Effect Senmr. Voltage will be lowwnan vane 1s passing through M c h .

Page 94: 61689121 Automotive Engine Electronics

ECM VOLTAGE IDENTIFICATION CHART

VOLTAGE 2.OL "J" BODY

VOLTAGE

KEY ION

I ENG ~ P E N I I I blNI CIRCUIT

KEY ENG OPEN I I RuN1cK-r. I I RUN 1 CKT. I CIRCUIT I P 'N]NOTE

113.4 1 I Fuel Pump Relay IAI 1 1 Not Used A2

On 12.2 A/C Relay on 13.8 A3

61 Battery 12v Input ~2 Voltage Monitor

b3 1 HE1 Ground l o l o 1 I Not Used

13.6 Ign. -- ECM Fuse

11.9

0

b4 1 Not Used I I I I I I 1 I

c; I Distributor Reference 1 0 1 .8 1 0 I

13.7

13.9

0-3 TCC Control or m/t shift light A7 2.5 .1 4.5

ALCL -- Serial Data A8

12.1

0

37 Not Used

38 A/C Signal

Coolant & TPS Ground ~ 1 1

11 31 1 Not Used

.1 0 System Ground IAI 2 Not Used

ID1 I System Ground 0 1 0 .1

I

Not Used C12

~2 MAP Ground 0 0

03 Ground

.45

4.9

1 1.9

~5 EST Bypass Signal 4.5 4.5 0

~6 Oxygen Sensor Ground .1 .1 0

! 07 Oxygen Sensor Signal .2 .5 0

08 Not used

.45

4.9

13.7

IDl31 Not Used I I r- ---

015 N O ~ used

lD1 6 Fuel Injector Driver 12.3 13.2 12.1

.1

.1

12.1

NOTES & SPECIAL INFORMATION VOLTAGE TESTING REQUIREMENTS:

TPS Sensor Signal

TPS 5v Reference

Not Used

Battery 12v Input

[I] Fuel pump relay will read 12v for 2 seconds when ignition is witched on. [2] VoRage reading variea [3] V a r b fmm .4!5 vo4i to batlory voh depending upon drhw wheel pamion. [4] Vadea Mth temperature. [5] Engine funning whage will be high or low depending if A/C Is on or off. [B] Note w b g e change when shifted into gear for automatic transmission. m Hall Effact Sensor. VoRage will be low when vane is passing through witch.

C13

C14

C15 C16

1) This chart is for use with a digital multimeter. 2) Engine must be at operating temperature. 3) Mle engine in "Closed Loop" for ENG RUN voltages. 4) Diagnostic test terminal in ALCL not grounded. 5) No "Scan" tools installed. 6) "Key On" readings represent known good battery.

Page 95: 61689121 Automotive Engine Electronics

W 4 ECM VOLTAGE IDENTIFICATION CHART

2.8L LB6 "A & J" BODY VOLTAGE VOLTAGE

NOTE

1

5

7

2 5

3 6

7 4

NOTES & SPECIAL INFORMATION VOLTAGE TESTING REQUIREMENTS:

(I ] Fuel pump relay will mad 12vfor 2 seconds when ignition is switched on. (21 Voltage reading varies. (31 Var* from .45 volt to battery w k depending upon drive wheel position. (41 Vanes with temperature. 151 Engine funning vokage will be high or low depending if A/C is on or off. [8] Note voltage change when shifted into gear for automatic transmisaton. m Hall Effect Sensor. Voltage will be low when vane IS passing through switch

1) This chart is for use with a digital multimeter. 2) Engine must be at operating temperature. 3) Idle engine in "Closed Loop" for ENG RUN voltages. 4) Diagnostic test terminal in ALCL not grounded. 5) No "Scan" tools installed. 6) "Key On" readings represent known good battery.

Page 96: 61689121 Automotive Engine Electronics

W 5 ECM VOLTAGE IDENTIFICATION CHART

VOLTAGE 2.8 L "F" BODY

VOLTAGE

N O T E

1

1

2 5

3 8

4

NOTES & SPECIAL INFORMATION

CIRCUIT

Battery 12v Input

Voltage Monitor (fuel pump:

HE1 Ground (EST ref low)

EST Control

Reference

Mass Airflow Sensor

Not Used

A/C Signal

Power Steering Pr. S/H

Park Neutral Switch :$-, Not Used

Not Used

KEY ENG ON I RUN I

VOLTAGE TESTING REOUIREMENTS:

[I] Fuel pump relay will read 12v tor 2 reconds when ignRlon is switched on. [2] Vonage reading mi-. [3] Varier horn .B wll to battery wll depending upon drive wheel portlion. [4] Varies with temperature. [5] Engine tunning wnage Mil be high or low depending If A/C is on or off. [el Note wnage change when shllled into gear for automatic transmimion. [7] Hall Effect Sensor. Voltage Mli be low when vane is w i n g through owitch. [a] Mewred between terminals C13 and 013.

D l 2

~ 1 3

~ 1 4

~ 1 5

~ 1 6

1) This chart is for use with a digital multimeter. 2) Engine must be at operating temperature. 3) Idle engine in "Closed Loop' for ENG RUN voltages. 4) Diagnostic test terminal in ALCL not grounded. 5) No "Scan" tools installed. 6) "Key On" readings represent known good battery.

Not Used

TPS,CTS,MAT Ground

Fuel lnjectors 2-4-6

Fuel lnjectors 2-4-6

Fuel lnjectors 1-3-5

0

12.2

12.2

12.2

0

13.8

13.8

13.8

Page 97: 61689121 Automotive Engine Electronics

W 6 ECM VOLTAGE IDENTIFICATION CHART

VOLTAGE 2.8L "P" FlERO

VOLTAGE

KEY ENG ON lRuN

I I I I I KEY I ENG I CIRCUIT PIN =IN CIRCUIT ON RUN

N O T E

Fuel Pump Relay A1 1 ~1 Battery 12v Input 11.9 13.7

Not Used A2 B2 NotUsed

Not Used A3 B3 HE1 Ground (EST ref low) 0 0

EGR Control A4 B4 ESTControl 0 1.3 - - . - .

Service Engine Soon I A ~ B5 Reference 0 1.6

Ign. -- ECM Fuse 1 ~ 6 ] 6 I Not Used I I

Shift Light M/T

ALCL -- Serial Data

I IF37 I Not Used I I

8 I A/C Signal On TXT n 12.2 n 13.8

ALCL -- Diag. Terminal CI MAT Signal 7~4 System Ground hi 2 1

Not Used IDA I System Ground 1 0 10 I

1 Not ~shable 1 ldle Air Control - - A - - ~ i g h k5 1 5 1 EST Bypass Signal 1 0 14.5 I 1 ~ 6 1 Oxygen Sensor Ground ( o 10 1

2 1~~ ( Oxygen Sensor agnal 1 .2 1.5 I 1 ~ 8 1 EGR Diagnostic s/w ( 12.2 11 3.8 1

Not Used

Not Used

I I ( Not Used

c 7

C8

Coolant Temperature

MAP Signal

MAP Signal ~1 2

Dl3 TPS Sensor Signal

TPS, CTS Ground

MAT, MAP Ground

TPS 5v Reference D l 4

D l 5 Fuel Injectors 2-4-6

-

0

0

0

0

Fuel Injectors 1-3-5

Fuel Injectors 1-3-5

Battery 12v l nput 01 6 - -

NOTES & SPEClAL INFORMATION

12.2

12.2

VOLTAGE TESTING REQUIREMENTS:

13.8

13.8

Fuel lnjectors 24-6

[ I ] Fuel pump relay will read 12vfor 2 seconds when ignition is switched on. [2] Vokage reading v a r i . 131 Vanes from .8 wit to battery wn depending upon drive wheel position. 141 Varies A h temperature. [5] Engine ~ n n l n g vdlage will be high or larr depending If A/C is on or off. [6] Note wnage change whan rhifted into gear for automatic transmission. [7] Hall E f f d Sensor. Voltage Mli be low when vane is passing through switch. [B] Measured betwen terminals C13 and D13.

1) This chart is for use with a digital multimeter. 2) Engine must be at operating temperature. 3) ldle engine in "Closed Loop" for ENG RUN voltages. 4) Diagnostic test terminal in ALCL not grounded. 5) No "Scan" tools installed. 6) "Key On" readings represent known good battery.

12.2 13.8

Page 98: 61689121 Automotive Engine Electronics

ECM VOLTAGE IDENTIFICATION CHART W 7

VOLTAGE 3.OL "N & H" BODY

VOLTAGE

N O T E

1

5

7

2 5

3 8

7 4

NOTES & SPECIAL INFORMATION

[ I ] Fuel pump relay will read 12vfor 2 seconds when ignaion is A c h e d on. 121 Voltaae readlna varies. "~ -

i3j ~ a r i i f r o r n .45 wH to battery voll depending upon drive wheel position. [4] Varia with temperature. [S] Engine Nnning wnage will be high or low depending if A/C is on or off. [a] Note wnage change *en shifted Into gear for aulomallc transmission. m Hell Effect Sensor. Voltage will be law when vane is passing through witch. 181 X Body only

D l

D2

D3

04

D5

D6

VOLTAGE TESTING REQUIREMENTS:

2

1) This chart is for use with a digital multimeter. 2) Engine must be at operating temperature. 3) Idle engine in "Closed Loop" for ENG RUN voltages. 4) Diagnostic test terminal in ALCL not grounded. 5) No "Scan" tools installed. 6) 'Key On" readings represent known good battery.

Ground

Coolant Fan Control

Cylinder Select for 6 cyl

Not Used

EST Bypass Signal

Oxygen Sensor Ground

D7

D8

D9

Dl0

D l 1

D l 2

D13

D l 4

D l 5

D l6

0

12

11.9

4.5

.1

Oxygen Sensor Signal

Not Used

Not Used

Ground

Power Steering Switch

TPS/CTS/ATS Ground

Ground

Fuel lnjector Cy12-4-6

Fuel lnjector Cyl 1-3-5

Fuel Injector Cy12-4-6

-

0

.1

13.7

4.5

.1

.2

.1

12.0

0

.1

1 1.9

1 1.9

1 1.9

- .1

0

12.1

0

0

Page 99: 61689121 Automotive Engine Electronics

W 8 ECM VO .TAGE IDENTIFICATION CHART

OLTAGE 3.8L A, C AND H BODY STYLES

v

N O T E

1

5

7

2 5

3

7

Not Used

Not Used C1 c2

Dl

D2

Ground 0

Coolant Fan Control 12

.8

10.6

D3

D4

D5

D6

D7

D8

D9

I -

.1 I 4th Gear Switch IC8

.8

12.3

Cylinder Select for 6 cyl

Not Used

EST Bypass Signal

Oxygen Sensor Ground

Oxygen Sensor Signal

Not Used

Not Used

10.6

.8

.1

I 0 1 13.5 ( 0 I Cruise Control ~ C S I 1 2.0 1 2.2 1 .1 1 Coolant Temperature l C I O l

0

0

12.3

.8

.1

I I - -

2.5 1 2.0 ( 0 1 Manifold Air Temp. 1 ~ 1 1

Idle Air Control --B--Low

Idle Air Control --B--High

0

0

0

.45 .1 TPS Sensor Signal C13 4.9 .1 TPS 5v Reference C14

~3

(-4

-

Dl 1

Dl2

Idle Air Control --A--High

Idle Air Control --A--Low

EGR Vacuum Diag. Sw.

~5

~6 c7

-

Power Steering Switch

TPS/CTS/ATS Ground

Dl 3

Dl 4

12.0

0

12.0

11.9

NOTES & SPECIAL INFORMATION

TPS/CTS/ATS Ground

Fuel Injector, Cyl 1

Dl 5

Dl 6

VOLTAGE TESTING REQUIREMENTS:

0

11.9

13.2

13.7

11 Fuel pump relay will read 12vfor 2 ssconds when ignition is .witched on. 2) VoHage reading ha. 31 V a r i from .45 wH to battery w H depending upon drive wheel position. 4) Varier with temperature. 51 Engine running voHage will k high or low depending If A/C is on or off. 81 Note voltage change when shifted into gear for automatic transmission. 71 Hall Effect Sensor. Voltage wlll be low when vane is passing through witch.

Fuel lnjector, Cyl3

Fuel Injector, Cyl4

1) This chart is for use with a digital multimeter. 2) Engine must be at operating temperature. 3) ldle engine in "Closed Loop" for ENG RUN voltages. 4) Diagnostic test terminal in ALCL not grounded. 5) No "Scan" tools installed. 6) "Key On" readings represent known good battery.

12.1

12.1

11.9

11.9

Fuel Injector, Cyl 2

Battery 12v Input C15

C16

Page 100: 61689121 Automotive Engine Electronics

ECM VOLTAGE IDENTIFICATION CHART

3.8L TURBO GRAND NATIONAL "G" BODY VOLTAGE VOLTAGE

KEY ENG ON lRuN OPEN CKT. I CIRCUIT

KEY ON CIRCUIT

0 I Fuel Pump Relay Battery 12v lnput ;;:; 1 A/C CIutchControl

Canister Purge Control 3 Crank Reference Low A' + :;:; 1 EGR control

Service Engine Soon

Ign. -- ECM Fuse

Crank Reference High

Mass Air Flow Sensor

1~2.2 1 ALCL -- TCC control

ALCL -- Serial Data

A9 Not Used .1 I ALCL -- Diag. Terminal

Vehicle Speed Sensor El Park Neutral Switch $-, 11 Not Used

0 Ground bid Fuel Injector, Cyl 5

12.0 13.2 12.1 Fuel Injector, Cyl 6 c12 .45 .45 .1 TPS Sensor Signal C13 4.9 4.9 .1 TPS 5v Reference C14 12.0 13.2 12.1 Fuel Injector, Cyl 2 C15 11.9 13.7 12.1 Battery 12v Input C16

ID1 I Ground

lD2 1 Coolant Fan Control 1 12 ( .1 1 0 Wastegate Controll 1 1.9 13.7 12.1

Not Used

lD5 1 EST Bypass Signal 14.5 14.5 10

Oxygen Sensor Signal

Not Used

EGR Diagnostic S/W

Ground

Power Steering Switch

TPS/CTS/ATS Ground

Not Used

Fuel Injector, Cyl 1

Fuel Injector, Cyl 3

Fuel Injector, Cyl 4

NOTES & SPECIAL INFORMATION VOLTAGE TESTING REQUIREMENTS:

:I] Fuel pump relay will read 12v for 2 sewnds when ignition is switched on. 121 VoHage reading varlea. :3] Varies from .45 volt to battery volt depending upon drive wheel position. :4] Varies A h temperature. :5] Engine running voltage will be high or low depending WA/C Is on or off. :8] Note voltage change when shifted Into gear for automatic transmission. 71 Hall Effect Sensor. Voltage will be low when vane Is p i n g through switch.

1) This chart is for use with a digital multimeter. 2) Engine must be at operating temperature. 3) Idle engine in 'Closed Loop" for ENG RUN voltages. 4) Diagnostic test terminal in ALCL not grounded. 5) No "Scan" tools installed. 6) "Key On" readings represent known good battery.

Page 101: 61689121 Automotive Engine Electronics

W 10 ECM VOLTAGE IDENTIFICATION CHART

VOLTAGE 4.3 L "B & G" BODY

VOLTAGE

KEY ENG ION I RUN I CIRCUIT

1 12.4 1 0 1 Canister Purge Control 1 ~ 3 I

0

S I ALCL -- Serial Data

13.4

.1

1 4.9 1 4.9 1 ALCL -- Diag. Terminal 1~9 I

Fuel Pump Relay A1

Not Used A2

13.8

Not Used A4

Service Engine Soon A5

.5

0

Not Used c12

.5 .5 TPS Sensor Signal C13

4.9 4.9 TPS 5v Reference C14

12.2 13.7 Fuel Injector "B" Driver C15

12.2 13.7 Battery 12v Input C16

.1

NOTES 81 SPECIAL INFORMATION

.5

0

( I ] Fuel pump relay will read 1% for 2 seconds when ignition is switched on. [2] Voltage reading varies. (31 Varies from .8 wil to banery wil depending upon drive wheel posttion. [4] Varies wllh temperature. (51 Engine running wilage will be high or low depending If A/C is on or off. (61 Note wltage change whan ~htfted into gear for automatic transmiasion. (7) Hall Efied Sensor. Voilage will be low when vane is passong through switch.

.1

1 KEY I ENG 1

Vehicle Speed Sensor

Coolant & TPS Ground

System Ground 1 ~ 1 2

I N O T E p " ! ClRCUlT I ON I RUN I

A1 0

A1 1

Battery 12v lnput

Not Used

ESC Signal

8 1 A/C Signal 122 13.8 m 0 0

I I I b9 I EGR Temp Diag. s/w ( 12.3 113.8 1

b111 Not Used I I I BlO

h121 Not Used I I I

D l2 NotUsed

D13 Not Used

D l 4 Fuel Injector "B" Driver 12.2 13.7

Dl5 Fuel Injector " A Driver 12.2 13.7

Dl6 Fuel Injector "A Driver 12.2 13.7

- . PIN

Park Neutral Switch ( A ~ - J D

VOLTAGE TESTING REQUIREMENTS:

1) This chart is for use with a digital multimeter. 2) Engine must be at operating temperature. 3) Idle engine in "Closed Loop" for ENG RUN voltages. 4) Diagnostic test terminal in ALCL not grounded. 5) No "Scan" tools installed. 6) "Key On" readings represent known good battery.

y2.3 o 13.7

Page 102: 61689121 Automotive Engine Electronics

W 11 ECM VOLTAGE IDENTIFICATION CHART

VOLTAGE 5.OL, 5.71 "F" BODY

VOLTAGE

CIRCUIT

12.2 13.8 Air Switch (Port Solenoid) A2 1

12.2 o Canister Purge A3

1 12.2 1 0 1 EGR control I A ~ 1

I I - I

Shift Ught M/T 12.2 1 13.8 ( TCC ControiA/T I A ~

.1

12.2

1.6 1.6 ( Vehicle Speed Sensor IAI 0 1 3 6

13.8

13.8

4.3

4.9

10 1 0 1 MAF Analog Ground ~AI 1 I 10 10 1 System Ground 1~121 2

Service Engine Soon .

Ign. -- ECM Fuse

2.5 ,

4.9

A5

A6

NOTES & SPECIAL INFORMATION

ALCL -- Serial Data

ALCL -- Diag. Terminal

2.5 2.1 MAT Signal c12

I ] Fuel pump relay will read 12vtor 2 seconds when ignition Is switched on. 21 Vonage madlng varier. 3) Varies from .8 wn to battery wn depending upon d h wheel position. :4] Varier with temperature. :5] Englne wnning wnage wlll be high or low depending if A/C Is on or off. :8] Note wnage change when shined into gear for automatic transmission. 71 Hall Effect Sensor. Vonage will be low when vane is passing through switch. 81 + or - .075V mee~ured betwen C13 and Dl2 91 OVwith circuit closed by a/c high pressure switch.

.55

4.9

12.2

11.9

1 Battery 1% Input 11.9 13.7

2 Fuel Pump Signal 0 13.8

A8

A9

63 HE1 Ground (EST ref low) 0 0

84 Not Used

2 5

.55

4.9

13.8

13.8

b5 I Reference 1 0 11.6 I

TPS Sensor Signal

TPS 5v Reference

EGR Diagnostic s/w

Battery 1% Input

B6

87

C13

C14

C15

C16

El 01 Park Neutral Switch zh ,, 1 2:i3 1 :3,7 1 11 Not Used

12 MAF Sensor Input .4 to 1

8

g

Not Used

ESC Sensor Signal

VOLTAGE TESTING REQUIREMENTS:

A/C Signal On Off

Not Used

DI2

Dl3

D l4

D l 5 ~ 1 6

1) This chart is for use with a digital multimeter. 2) Engine must be at operating temperature. 3) Idle engine in "Closed Loop' for ENG RUN voltages. 4) Diagnostic test terminal in ALCL not grounded. 5) No "Scan" tools installed. 6) "Key On" readings represent known good battery.

9.2 9.2 12.2 0

Burn-Off Relay Control

Notused

Notused

Fuel Injectors 1-3-5-7

Fuel lnjectors 2-4-6-8

13.8 0

0

12.2

12.2

0

13.8

13.8

Page 103: 61689121 Automotive Engine Electronics

W 12 ECM VOLTAGE IDENTIFICATION CHART

VOLTAGE 5.OL LB9 "F" BODY

VOLTAGE

N O T E

1

1

7

2 5

3 6

4

NOTES & SPECIAL INFORMATION VOLTAGE TESTING REQUIREMENTS:

[ I ] Fuel pump relay will mad 12vfor 2 seconds when ignition is mltched on. [Z] Vohage mading varies. [3] Varies from .45 w h to battery wtl depending upon drive wheel position. [4] Varies with temperature. 151 Engine running whage will be high or low depending If A/C Is on or off. [6] Note whage change when shied into gear for automatic transmission. PI Hall Effect Sonsor. Vonage wlll be iow when vane is passing through switch.

1) This chart is for use with a digital multimeter. 2) Engine must be at operating temperature. 3) Idle engine in "Closed Loop" for ENG RUN voltages. 4) Diagnostic test terminal in ALCL not grounded. 5) No "Scan" tools installed. 6) "Key On" readings represent known good battery.

Page 104: 61689121 Automotive Engine Electronics

ECM VOLTAGE IDENTIFICATION CHART

VOLTAGE 5.7L LB9 "Y" CORVETTE

VOLTAGE

KEY ENG PEN loN 1RuNfkT . I cmcun-

I I 1 KEY I ENG

0

12.4

12.4

I b 1 I Battery l2v lnput 1 11.9 1 13.7 N O T E

IN

13.9

13.9

13.8

-- - -

2 Fuel Pump Signal 0 13.9

3 EST Reference Low 0 0

CIRCUIT

0

12.2

7 Distributor Reference

12.4

.1 - 13.3

ON

Fuel Pump Relay

Air Switch -- Port Solenoid

Canister Purge Control

~ALCL -- Serial Data 1 ~ 8 1

RUN

A1

A2

A3 13.8

13.8

13.6

12.4 13.8 0

14.9 14.9 1.1 ~ALCL -- Diag. Terminal 1 ~ 9 I

M/T Ovedrive or A/T TCC Control I ~7

2 5

Not Used

12.2

12.2

12.1

EGR Control

Service Engine Soon

Ign. -- ECM Fuse

.5

0

.1 .1 0 Ground 1 ~ 1 2 )

A4

A5

A6

3 C

s11

.5

0

OPEN CKT.

12.1

0

0

0 12.2 0

0 0 Park Neutral Switch :&

NotUsed

4 MAF Sensor Input

NOTES & SPECIAL INFORMATION VOLTAGE TESTING REQUIREMENTS:

.6

[I] Fuel pump relay will read 12vfor 2 seconds when ignition is switched on. (21 Voilage reading varies. [3] Varies from .45 van to battery volt depending upon drive wheel position. 141 Varies with temperature. [S] Engine ~ n n i n g wnage will be high or low depending if A/C Is on or off. 161 M e Mitage change when shiftad into gear for automatic transmisrrion. m Hall E f f d Sensor. Vonagewill be low when vane is parsing through Jwitch.

0 12.3

2.5

1) This chart is for use with a digital multimeter. 2) Engine must be at operating temperature. 3) Idle engine in "Closed Loop" for ENG RUN voltages. 4) Diagnostic test terminal in ALCL not grounded. 5) No *Scanu tools installed. 6) "Key On" readings represent known good battery.

Vehicle Speed Sensor

MAF Sensor Ground

0 13.7

.4 - 1

A1 0

A1 1

Page 105: 61689121 Automotive Engine Electronics

W 14 ECM VOLTAGE IDENTIFICATION CHART

NOTES 8

VOLTAGE 5.7L "Y" CORVETTE 1985

VOLTAGE

CIRCUIT

Fuel Pump Relay

I I I I KEY I ENG I

N O T E IN

112.2 1 0 1 Canister Purge 1~3 I

1

b3 1 HE1 Ground (EST ref low)l 0 1 0 1

CIRCUIT

EGR Control

A6

B l

I

Shin Ught M/T 12.2 1 13.8 1 TCC Control AD 1 ~ 7

ON

1 8 2

R U N

Battery 12v Input

Fuel Pump Signal

11.9

- -

64

B5

~6

B7 4.3

4.9

.6

0

13.7

0

0

0

9.2

- --

EST Control

Reference (EST Ref Hi)

Not Used

ESC Sensor Signal

2 5

13.8

-- -

1.3

1.6

9.2 2.5 ,,

4.9

.6

0

10

11

88

0

2

9

4

8

8

SPECIAL INFORMATION VOLTAGE TESTING REQUIREMENTS:

ALCL -- Serial Data

ALCL -- Diag. Terminal

Vehicle Speed Sensor

MAF Analog Ground

sg

12 0 I System Ground IAI 2

[ I ] Fuel pump relay will read 12v for 2 seconds when ignition Is witched on. [2] Voitage reading varier. [3] Varies from .6 vok to battery volt depending upon drive wheel position. [4] Varies with temperature. [5] Engine mnning voltage will be high or low depending If A/C is on or off. [6] Note witage change when shifted into gear tor automatic transm~ssion. [7] Hall E f f d Sensor. Voltage will be low when vane is passing through switch. [8] + or - .075V measured between C13 and Dl2 [Bl OV with c~rcult closed by a/c h~gh pressure svntch.

J

A8

A9

A1 0 A1 1

Not Used

A/C Signal off On

- 0 13,7

.4 to 1

Park Neutral Switch zk MAF Sensor

Not Used I I

1) This chart is for use with a digital multimeter. 2) Engine must be at operating temperature. 3) Idle engine in "Closed Loop" for ENG RUN voltages. 4) Diagnostic test terminal in ALCL not grounded. 5) No "Scan" tools installed. 6) "Key On" readings represent known good battery.

- - -

0 12,3

2.5

o 12.2

o 13.8

Page 106: 61689121 Automotive Engine Electronics

ECM W 15

VOLTAGE IDENTIFICATION CHART

VOLTAGE 2.5 L SIT TRUCK M VAN

VOLTAGE

N O T E

1

1

2 5

3 8

NOTES & SPECIAL INFORMATION

3.5 1.2 MAP Sensor Signal (211 2.5 2.2 Manifold Air Temp Sensor C12

[I] Fuel pump relay will read 12vfor 2 seconds when ignition is switched on. [2] Voltage reading varies. [3] Varies from .45 volt to batiery wH depending upon driva wheel position. [4] Vatim with temperature. [SJ Englne ~ n n l n g voltage will be high or low dependlno If AIC Is on or off.

.45

4.9

1 1.9

[6] ~ o i e voltage change when shntez Into gear for aulo~atlc'transmission. [7] Hall Ened Senaor. Voltage will be low when vane Is passing through switch.

.45

4.9

13.7

VOLTAGE TESTING REQUIREMENTS:

Dl2

~ 1 3 ~ 1 4

015 DI 6

1) This chart is for use with a digital multimeter. 2) Engine must be at operating temperature. 3) Idle engine in "Closed Loop" for ENG RUN voltages. 4) Diagnostic test terminal in ALCL not grounded. 5) No "Scan" tools installed. 6) "Key On" readings represent known good battery.

TPS Sensor Signal

TPS 5v Reference

Not Used

Battery 12v Input

Not Used

NotUsed

Not Used

Not Used

Fuel Injector "A" Driver

C13 C14

C15

C16 12.2 13.7

Page 107: 61689121 Automotive Engine Electronics

W 16 ECM VOLTAGE IDENTIFICATION CHART

VOLTAGE 4.3L, 5.OL, 5.7L, 7.4L TRUCK

VOLTAGE

KEY ENG ION I RUN I CIRCUIT

0 13.4 Fuel Pump Relay A1

Not Used A2

Not Used

12.4

1 13.3 1 13.6 ( Ign. -- ECM Fuse 1 ~ 6 I 12.2 ( 13.8 1 TCC Control or M/T shift light I A ~ 1 ; 1 .5i:i 1 ALCL -- Serial Data 1:; 1 4.9 4.9 ALCL -- Diag. Terminal

Vehicle S ~ e e d Sensor A1 0 - - - - -

1 o 1 o [MAT &TPS Ground IAI i l .1 .1 System Ground 1 ~ 1 2

Not Used c12

.45 .45 TPS Sensor Signal C13

4.9 4.9 TPS 5v Reference C14

Not Used C15

1 1.9 13.7 Battery 12v Input C16

NOTES & SPECIAL INFORMATION

[I ] 12v for 2 reconds on 4.3 & 5.0 Land 20 seconds for 5.7 & 7.4 L [2] Voltage reading varies. [3] Varies from .45 wll to baliery voh depending upon drive whwl position. [4] Varies with temperature. [5] Voiiage measured between C13 and A1 1 (+ or - .05 V) [6] Note voltage change when shmed into gear for aulomatic transmission.

Also, darmshM control on THM 400. [7] Except 4.3 L M & G van. this system is wired at opposlte ends. [B] Nd used on 7.4 L

N O T E CIRCUIT

1 - - -

2 Voltage Monitor (fuel pump) 0 13.9

3 HE1 Ground (EST ref low) 0 0

0 10 Park Neutral Switch 2; ,, 12,3

11 Not Used

b121 Not Used I

VOLTAGE TESTING REQUIREMENTS:

1) This chart is for use with a digital multimeter. 2) Engine must be at operating temperature. 3) Idle engine in "Closed Loop" for ENG RUN voltages. 4) Diagnostic test terminal in ALCL not grounded. 5) No "Scan" tools installed. 6) "Key On" readings represent known good battery.

Page 108: 61689121 Automotive Engine Electronics

OXYGEN SENSOR CR(3UND

-5s nm now -u

V M C L E SPEED

CYLI-R YLCCT 6 C Y L M E R

CONSTANT BATTERY MLTACC

TWROTTLE POSITION SENSOR

3.8 L "C & H" BODY

VE-E WEED

SENSOR I - - GROUND m i

LCM - - FLn€

I

PARK 3

- - KIN. SWITCH - m m w o P i C R A N K I R U N ru-c LINK a+ MTTERY -

CIH 5w. RUN -- - - - m n z

A I C '=L7 CANISTER EDR FMI PVRCC CONTROL RELAY

A I C RELAY L 5 C M A F T C C POWER STCEWNa

PR s t w

F U n PUMP C 3 NJCCTOR

SWTCHEO I #-I-

Page 109: 61689121 Automotive Engine Electronics

R/C OH S I G M L

P O K R STEERING PRESSURE SWITCH

R/C CLUTCH C O M R O L

E6R DIRGHOSTIC SWITCH

E6R COHTROL S U I T C H

CRHISTER PURGE URLUE

"SERUICE EHGIHE SOOH- L I G H T

TCC COHTROL

4 T H GERR

CRH SIGHRL

I G H I T I o H

I::: CONTROL

FRH CONTROL

E C M

R/C DRSH SWITCH -7 r I t I

POWER SlEERW3 PRESSURE SIW

3.8 L "C & H" BODY

ECN FUSE F-.J$ ;;En* ,

- "SERUICE EHGIHE GAUGES FUSE - -

T I G H

H I G H PRESSURE SWITCH

COWRESSOR CASE GROUtQ

7 R BR8KE SWITCH E C ~ FUSE

3RD 6ERR S V I T C H

D I 8 7 ! T R R H S l l I S S I O H

I 4TH GERR SWITCH - I % I - .

@ "C" CRR W I L L USE RESISTOR. JUMPER WIRE W I L L BE USED

Page 110: 61689121 Automotive Engine Electronics

ECM EST REFERENCE BYPASS GROUND

IAC COlL "A" HI IAC COlL "A" LO IAC COlL "B" HI IAC COlL "B" LO

OXYGEN SENSOR SIGNAL

OXYGEN SENSOR GROUND

INJECTOR DRIVE

INJECTOR DRIVE

EGR DIAGNOSTIC TEMP. SWITCH

PARK NEUTRAL SWITCH (A/T)

VEHICLE SPEED SENSOR

A/C SIGNAL

MAGNETIC PICKUP & IGNITION MODULE

IAC VALVE

ENGINE GROUND

- -

Page 111: 61689121 Automotive Engine Electronics

5.0 LITRE

SERVICE ENGINE SOON LIGHT CONTROL DRIVER

TCC CONTROL A/T

EGR CONTROL

CANSITER PURGE

AIR CONTROL SOL.

AIR SWITCH SOLENOID

COOLING FAN CONTROL

ECM

1

ECM

A5

A7

A4

A3

c 2

A2

c 1

I

GAGES FUSE IGN. 12 V.

S.E.S. LAMP A

B BRAKE SWITCH

A B

AUTOMATIC

rn c TRANSMISSION

I D TCC SOLENOID

I

FIEJDCIBIA EGR SOLENOID

d &

CANISTER PURGE SOLENOID

(GRAY CONN.) DIVERT SOLENOID

P (BLACK CONN.)

PORT 1 - SOLENOID

I

FIEIDCIBIA , 1 I I , FAN CONTROL RELAY

B +

FAN B +

FUSE

E -

D -

C

B - -

A

\ COOLING

1 - FAN - -

Page 112: 61689121 Automotive Engine Electronics

ECM DIAGNOSTIC TEST

SERIAL DATA

SYSTEM GROUND

SYSTEM GROUND

SYSTEM GROUND

COOLING FAN REQUEST, HIGH A/C PRESSURE

MAT SIGNAL

5 V. REFERENCE

TPS SIGNAL

5V. RETURN

COOLANT TEMP SENSOR SIGNAL

Page 113: 61689121 Automotive Engine Electronics

5.0 LITRE

ECM 12 VOLT 12 VOLT

FUEL PUMP A1 RELAY DRIVER (+ 12 VOLT)

SYSTEM GROUND A12

FUEL PUMP VOLTAGE MONITOR

SYSTEM GROUND

MAF SIGNAL

~1

ANALOG GROUND

BURN-OFF CONTROL

~ 1 1

FUSE & HOLDER - - - - - - -

I

PUMP FUEL

OIL PRESSURE

I I - - - SWITCH

POWER R E L T iA 94 , MAF SENSOR

BURN-OFF RE LAY

E -C

ENGINE GROUND

MAF SENSOR B

Page 114: 61689121 Automotive Engine Electronics

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- +

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