YYou’re probably already awareof just how stringent the rulesfor air quality are here in

California. Chances are you also knowthat no matter what laws they pass orwhat rules they put in place, the smog isstill going to be with us.

What you may not be familiar withis what some manufacturers are doingto help alleviate these conditions… andhow drivability diagnosis just got a lit-tle tougher, because of today’s OBD-IIregulations. We’re seeing more andmore driveability problems on theATRA HelpLine; what’s surprising ishow few technicians really understandtoday’s On-Board Diagnostic systems,and how they affect powertrain opera-tion. In this issue of Let’s Play Ball,we’ll cover some of the definitions andchanges to the OBD-II rulebook, andhow those new rules are making it hard-

er and harder to hit one out of the diag-nostic park.

The Facts about OBD-IIThe California Air Resources

Board (CARB) began regulation of OnBoard Diagnostic II (OBD-II) for dieselvehicles sold in California beginningwith the 1997 model year. In reality,OBD-II first began showing up in gaso-line-powered passenger cars in 1994.

OBD-II requires today’s vehiclecomputers to monitor all emission-related components (fig 1). TheMalfunction Indicator Lamp (MIL) hasto light and alert the driver of the needfor service to the emission control sys-tem. A Diagnostic Trouble Code (DTC)is associated with the MIL, identifyingthe specific area of the fault. Today, theOBD-II system is required for all vehi-cles under 14,000 GVW — gas and

diesel.The OBD-II system meets govern-

ment regulations by monitoring theemission control system. Generallyspeaking, when a system or componentfails or goes far enough out of range tocause the vehicle to exceed emissionthresholds, the computer lights the MILand stores a DTC in memory.

Diagnostic Trouble Codes (DTCs)Here’s how OBD-II systems moni-

tor and indicate system faults. Thecomputer monitors the system for faultsduring a drive cycle — a specific seriesof operating conditions (more aboutdrive cycles later):

• The first time the computer detects aproblem, it sets a pending DTC inthe computer’s keep-alive RandomAccess Memory (RAM).

24 GEARS August 2004

ON-BOARD DIAGNOSTICSFOR THE FORD DIESELON-BOARD DIAGNOSTICSFOR THE FORD DIESEL

LETS PLAY BALL

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• After two consecutive drive cycleswith the fault present, the computerturns the MIL on and sets a DTC.

• Once a monitor lights the MIL, thevehicle must go through three con-secutive drive cycles without thefault for the MIL to turn off.

• The computer clears the DTC auto-matically after 40 drive cycles with-out the fault appearing, once the MILis turned off.

The OBD-II diagnostic computerprogram in vehicle computer coordi-nates the OBD-II self-monitoring sys-tem. This program controls all monitorsand interactions, DTC and MIL opera-tion, freeze frame data, and scan toolinterface.

Freeze Frame is a valuable diag-nostic tool that captures scan data at themoment the computer stores the first

DTC in memory. This data is accessiblewith the scan tool to assist in repairingthe condition that cause the DTC to set.

OBD-II Inspection andMaintenance (IM) readiness DTCP1000 indicates that not all of the OBDmonitors have been completed since thecomputer’s keep-alive RAM was lastcleared. In some states, it may not bepossible to obtain vehicle registrationor pass an emission’s inspection ifP1000 is still in memory. To erase DTCP1000, operate the vehicle through themanufacturer’s specified drive cycle,until the computer goes through a fullset of monitors and identifies propersystem operation.

Drive CyclesSpecific drive cycles can vary

between manufacturers and systems(Fig 2). OBD-II standards for a drive

cycle include:1. Start and warm the engine to approx-

imately 180ºF (ECT at 180°F for atleast 4 minutes).

2. Let the vehicle idle for 45 seconds. 3. From a stop, accelerate to 45 mph at

1/4 throttle; about 10 seconds.4. Steady throttle between 30-40 MPH

for 60 seconds.5. Drive 20-40 MPH (no WOT) for

about 4 minutes.6. Decelerate to a stop and idle for 10

seconds.7. Accelerate to 55 MPH at 1/2 throttle;

about 10 seconds8. Steady the throttle between 40-60

MPH, posted speed limit for 80 sec-onds.

The specific order and duration ofthese conditions will vary from manu-facturer to manufacturer.

GEARS August 2004 25

PART 1PART 1

by Lance Wiggins

Figure 1 – All of these are systems in the vehicle.All of them have monitors

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26 GEARS August 2004

OBD-II System MonitorsThe OBD-II systems monitors

include:• OBD-II Trip Monitor• Comprehensive Component Monitor

• Glow Plug Monitor• Misfire Detection Monitor• Exhaust Gas Recirculation (EGR)

Monitor• Catalyst Converter Monitor

As you can see, OBD-II provides

many different ways to identify a sys-tem failure, as long as all the stars arelined up… but what happens whenthey’re not?

In the 2001 ATRA technical semi-nar, we discussed codes P0603 (RAM)

On-Board Diagnostics for the Ford Diesel, Part 1

Figure 2

Comprehensive Component and EGR Monitor

DriveInstruction

Start andWarm Eng.

ECT @180oF

IdleAccel.

to 45 MPH1/4 Throttle

SteadyThrottle

30-40 MPH

Drive20-40 MPH(No WOT)

DecelandIdle

Accelto 55 MPH1/2 Throttle

SteadyThrottle

40-60 MPHPostedSpeed

TimeAt Least

4 minutes

OBD-II Trip

OBD-II DRIVE CYCLE

Misfire and Adaptive Fuel Monitors

Catalyst Efficiency M

onitor

HO2S Monitors

45 Seconds 10 Seconds 60 Seconds 4 Minutes 10 Seconds 10 Seconds 80 Seconds

LetsPlayBall0804.qxd 7/21/04 2:55 PM Page 26

GEARS August 2004 27

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Random Access Memory failure andP0605 (KAM) Keep Alive Memoryfailure. If any one of these codes ispresent, there’s a good chance youwon’t be able to get codes from thecomputer because of a memory loss.Something else that can interfere withOBD-II monitors and codes is if thecomputer isn’t receiving the proper

voltage, because of aftermarket deviceslike CB radios, police scanners or aux-iliary lighting. When a failure is presentand you can’t get codes from the com-puter, it’s time to monitor the differentareas of the OBD-II system.

In the next issue of GEARS, we’llcover the comprehensive diagnosticmonitors and how they relate to the

daily driving habits of your customer…and That’s the Game!

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