487987-Taking-Your-Scan-Tool-to-the-Next-Level

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Taking Your Scan Tool To The Next Level

new type of diagnostic software that looks at system efficiency, and system failures. OBD

II does this with a series of enhanced system monitors and faster processors. OBD II

standardizes many of the diagnostic procedures, as well as common terms and acronyms.

OBD II will even store a freeze frame of serial data in its own memory if an emissions-

related fault code is set! But for all of its new high-tech advances, you will still need a

high-quality DVOM and lab scope to properly diagnose this advanced system. The real

value of OBD II to the automotive repair technician is the diagnostic monitor software.

The major change in OBD II equipped vehicles for 1995 and 1996 will be in the vehicles

diagnostic software. The vehicles that are equipped with the "Leak Down" type of EVAP

diagnostic monitors will have the most noticeable amount of new hardware. This is

because of their new leak detection pump (LDP).

One other major change is the portion of the PCMs software used to control the advanced

system monitors, freeze frame data, MIL illumination and diagnostic trouble code (DTC)

storage. Chrysler calls this their Task Manager Software, General Motors calls it their

Diagnostic Management Software and Ford calls it their Diagnostic Executive Software.They basically do the same thing.

Trips And Drive Cycles

Technicians have had trouble understanding the difference between an OBD II trip and the

drive cycle. Here are the primary differences between them:

1. An OBD II trip is when the vehicle is started and brought up to 160 degrees

Fahrenheit and at least 40 degrees Fahrenheit above its original starting

temperature. It must then meet specific enable criteria for a diagnostic monitor to

start, run and show a pass or fail.

2. A drive cycle is the same as above, but, all of the diagnostic monitors must

complete and show a pass or fail result. The OBD II drive cycle is the complete

test running without interruption.

The value to the technician in all of this is that we can use these diagnostic monitors to

confirm the effectiveness of our repairs. This is the first time that we have had this kind of

diagnostic power in our hands. This should prove to be very helpful once technicians

understand the concept of how the OBD II diagnostic monitors work.

OBD II Freeze Frame Data

Another advantage of OBD II is the freeze frame data function of the scan tool. Whenever

an emissions related DTC is set, the MIL will illuminate and a freeze frame will be set in

the PCMs memory. The freeze frame should contain, but isnt limited to, the following

data:

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q Engine load (calculated)

q Engine RPM

q Short- and long-term fuel trim

q Vehicle speed

q Coolant temperature

q Intake manifold pressure

q

Open/closed loop operationq Fuel pressure (if available)

q DTC

The generic OBD II scan tool will be able to access this information any time a DTC is

recorded. But will this information really be that helpful? Im not so sure. If you have

freeze frame data, you must already have a DTC to work with. So if its a hard fault like a

Type A misfire, you probably wont need this extra data to diagnose this vehicle. But if

this is an intermittent problem, the freeze frame data could help narrow down the problem.

But would you want to put all of your faith in one frame of serial data? I would use thefreeze frame data to set up a road test with the operation conditions. This is what you

would do with an OBD I vehicle and the customers detailed complaint. Then you can use

OBD IIs next feature to do a proper diagnostic.

OBD II Data (No Codes)

In this generic scan tool feature, you cant get DTCs. But you can get a serial data stream

that will update a minimum of two times a second. More importantly, you will have

access to at least 16 data parameters and a 66-frame movie of ECU/PCM data. The most

important function of any scan tool is to diagnose intermittent problems. Listed below aremy reasons why the movie/snap-shot is so valuable!

1. On slower baud rate systems, an out-of-range sensor may take several frames of

data before a DTC is set. But it would still cause a noticeable driveability problem

on the vehicle. And it still might not set a DTC. Duplicating the customers

complaint with a road test and a movie/ snap-shot may be the only way to properly

diagnose the vehicle.

2. On newer systems with faster baud rate systems, the problem can be worse! Onthese faster systems, the scan tool data updates so fast that the scan tool display

cant keep up. So if you are looking for that TPS to drop out for a frame or two,

you may never see it happen. Thats because the scan tool is probably displaying

only one out of every three or five frames of data. The TPS could drop out and you

would never see it! Your scan tool is getting all of the data; its display just cant

keep up. So take a movie/snap-shot. Then you can play it back at a rate that your

scan tools display and brain can handle.



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Short- And Long-term Fuel Trim

To explain short- and long-term fuel trim parameters, re-visit block learn integrator

values. Basically they are the same thing. Block learn and integrator both have a range of

0 - 256 with 128 the mid-point. These are fuel trim commands from the PCM. If the value

is less than 128, the PCM command is lean. If the value is more than 128, the command is

rich. If the value is 128, there is no change in the fuel trim. The integrator is the short-term

or fast fuel adjustment in relationship to the O2 sensor reading. The block lean is the long-

term or learning/ adaptive adjustment to O2 sensor readings.

OBD II uses short and long term fuel trim values. The only difference is that 0 percent

replaces 128 as the mid-point for fuel trim adjustments. Any value over 0 percent the

PCM is responding to a lean O2 sensor reading by adding fuel. In general, short- and long-

term fuel trim commands should stay around +10 percent/-10 percent if the PCM is

controlling fuel properly. Your scan tool troubleshooting or diagnostic software will help

give you a better understanding of these values.

What other skills will you need?

As mentioned earlier, you need to understand electrical waveforms (lab scope) and have

access to electronic repair information. This could be a CD-ROM based repair system or

going online with your shop PC. Good training is out there if you look for it. Dont let

yourself or your shop get lost in the past!

Guy Garrett is an industry instructor based in Springboro, Ohio. He has more than 18

years experience in the automotive industry.

ASA Main Page || AutoInc. Main Page

NACE Pre-Show Coverage

Keeping Up With Industry Trends

Colin Powell Soldier, Leader ... Automotive Technician?

NACE Show Specials

How's Your Business? || Taking Your Scan Tool To The Next Level

Cruising Instead Of Abusing || Putting The Brakes On Payroll HeadachesWhats Ahead For The Collision Industry?

Guest Editorial -- The Mouse That Roared

Tech To Tech || TechTips || Stat Corner || News Briefs

Taking The Hill || Directions || Chairman's Message

AutoInc. Magazine , Vol. XLIV No. 11, November 1996

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487987-Taking-Your-Scan-Tool-to-the-Next-Level

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