OBD II Quick Overview - Gem State Gymnastics Academy forro...(ignition coils, solenoids, fuel...

Copyright © 2002 John ForroAll Rights Reserved

Manufactured in the United States

No part of this book may be reproduced, stored in a retrieval system,or transmitted, in any form by any means, electronic, mechanical,photocopying, recording, or otherwise, without prior written permis-sion of the authors.

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The following triple-distilled OBD II overview isdesigned to provide you with a general overview ofOBD II.

What is OBD II?

OBD II is a set of onboard self-tests designedto monitor vehicles during normal operation.The tests are designed to detect vehicle problemsthat could result in an increase in vehicle emissions.Standards for acceptable emission levels are basedon a Federal Test Procedure used to certify thevehicles when they are new.

OBD II(OnboardDiagnostics/ SecondGeneration)

Special onboardvehicle self-testsdesigned to detectincreased vehicleemissions

Onboard

Located in the vehicleinside the vehiclepowertrain computer(PCM).

Emissions

By-products of thecombustion processthat exit through theexhaust to theatmosphere

Important! OBD II is designed to monitor thevehicle during normal vehicle operation.

Tests run automatically, under exact conditions, eachtime the vehicle is driven.

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How does the monitoring system work?

The onboard system waits for vehicle operatingconditions to be just right before it will start to run itstests, known as Monitors.

Conditions needed to run monitors are met duringnormal driving. Specific modes of vehicle operationthat allow each monitor to run are called Trips.

If tests indicate that emissions have increasedbeyond a test limit, the onboard system records thefault.

How Do We Know if a Problem is Detected?

If the onboard system detects a problem that willresult in increased vehicle emissions, it alerts thedriver by turning on a dashboard warning light,known as the Malfunction Indicator Lamp (MIL).

At the same time the MIL illuminates, a code isstored in the vehicle’s powertrain computer.

OBD II codes are referred to as Diagnostic TroubleCodes (DTCs). We’ll use this term frequentlythroughout the remainder of this manual.

MIL

Malfunction IndicatorLamp, formerlyreferred to as theCheck Engine orService Engine SoonLight

Monitors

Tests run by theonboard diagnosticsystem

Trips

Driving conditions thatallow a monitor to run

DTC

Diagnostic TroubleCode is a specific faultdefinition stored in thecomputer’s memorywhen a monitordetermines that avehicle problem willresult in increasedemissions

Trips, Monitors, DTCs, and the MIL

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What does the Onboard system test?

The onboard system tests individual components tosee if they are experiencing any electrical problems.Components tested include individual sensors(ECT, IAT, TP, MAP, etc.) and some actuators(ignition coils, solenoids, fuel injectors, etc.) Sensors

Electrical measuringdevices that providethe computer withinformation aboutvehicle operatingconditions

Actuators

Electrically operateddevices that do workin response to PCMcommands

Inputs

Electrical signals sentto the PCM.

Outputs

Commands FROMthe PCM to variousactuators

What kinds of tests are performedby OBD II?

The simplest and most familiar of all OBD II diag-nostics are electrical tests for short and opencircuits. Most of us are familiar with these tests andthe types of codes stored from our previous experi-ence with earlier vehicle self-diagnostics. OBD I

The first generation ofonboard diagnostics

OBD II tests muchmore than OBD I.

Open Circuit

An incompleteelectrical circuit. Theelectrical resistanceof an open is infinity.

Short Circuit

A condition wheretwo or moreconductors thatshould be insulatedfrom each othercome in contact.

Short circuits arecommonly the resultof damagedinsulation.

Inputs, Outputs, Shorts and Opens

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What else is OBD II testing?

OBD II also tests the catalytic converter and several“systems” that are directly responsible for reducingharmful vehicle emissions.

What are the test procedures called?

OBD II test strategies are referred to as Monitors.

When do Monitors run?

Some monitors are designed to run once per Tripand, when they have run to completion, their testresults are stored as a pass or fail in the PCM.

These are referred to as Non-continuousmonitors. Non-continuous monitors have

a beginning, a middle, and an end.

Non-continuous monitors run once per trip to testvehicle systems that are directly related to emissioncontrol: EVAP, EGR, AIR, Oxygen Sensor, andthe Catalytic Converter.

MonitorsOBD II tests

TripsDrivingconditionsthat allow amonitor to run

Non-ContinuousMonitorsMonitors thatrun once pertrip

EVAPThe Evaporativeemission systemcontains fuelvapors to preventtheir escape to theatmosphere.

EGRExhaust GasRecirculationintroduces ameasured amountof inert exhaust gasto the cylinders toreduce peakcombustiontemperatures.

AIRInjects air into theexhaust to promoteadditionalcombustion ofunburned fuel

Continuous and Non-Continuous Monitors

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Yes. In fact there are three monitors that run prettymuch all the time. These monitors stay “on duty”whenever the vehicle is being operated and arereferred to as Continuous Monitors, as a result.

There are three Continuous Monitors that will befound in all OBD II vehicles:

• Comprehensive Component Monitor• Fuel System Monitor• Misfire Monitor

ContinuousMonitors

Run continuously andare never listed asDone or Complete inReadiness Statuslist

ContinuousMonitor Types

• ComprehensiveComponent

• Fuel System• Misfire

Are there other Monitors?

Why do Continuous Monitors runcontinuously?

We just saw that Non-continuous monitors keep tabson vehicle systems that are primarily responsible foremission control. But these systems are basicallyadd-ons. They are not the core systems responsiblefor vehicle operation.

For example, the vehicle may run normally if there’sa leak in the EVAP system or if the catalyst stopsworking.

But problems with:• Comprehensive components (sensors or actuators)• Excessive Fuel Control• Engine Misfire (can result in a substantial increase in emissions).

Additionally, misfire can damage the catalyst. That’swhy these three critical areas of powertrain opera-tion are monitored continuously.

ComprehensiveComponents

Sensors andactuators

Fuel System Monitor

Tracks the PCM fuelcorrections needed tomaintain correct air/fuel ratio in closedloop

Misfire

Anything that preventscomplete combustion

Continuous Monitors

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Does anything else happen when a DTC isstored and the MIL is illuminated?

When the first DTC is stored, the PCM takes a“snapshot” of vehicle operating conditions at theinstant the code was set.

The Freeze Frame snapshot lists data param-eters that include important diagnostic informationabout critical engine conditions. This information isprovided for diagnostic purposes.

Freeze Frame

A ‘snapshot” list of keyvehicle parametersstored with the first orhighest priority DTC

Parameters Listed inFreeze Frame

• DTC number

• Fuel Loop Status(Open or ClosedLoop)

• Calculated EngineLoad

• Engine Coolant Tem-perature

• Short Term Fuel Trim

• Long Term Fuel Trim

• MAP

• Engine RPM

• Vehicle Speed

• Air Flow RateTypical Freeze Frame Data display

( EASE Diagnostics )

Freeze Frame

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Let’s stop here for a quick review!

OBD II is an onboard monitoring system that looks foremissions related problems

Monitors are test programs that check vehiclecomponents and systems during normal driving.

Some monitors run Continuously, whileothers are Non-continuous and run onceper trip.

Trips are specific driving conditions that let themonitors run. Trips definitions vary by monitor.

If a component or system fails a test, thetest results are sent to the PCM. ThePCM may store a Diagnostic TroubleCode (DTC) and turn on the MIL to alertthe driver that a fault has been detected.

We’ll return to this list and add additionalitems as we explain more about OBD II.

Let’s move on.

A Freeze Frame snapshot of criticalengine parameters is saved in thePCM memory with the first DTC stored.

Review

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Trips and Enabling Criteria

How do Trips allow Monitors to Run?

Each monitor needs certain test conditions so it canrun to completion and provide accurate test results.

These conditions are known asEnabling Criteria.

Most Trips include a Key-on, vehicle operating undercarefully defined conditions, followed by a Key-off.The Key-off is an important part of some trip defini-tions. Even though a code has been stored during atrip, the MIL may not illuminate until the next timethe ignition is switched on.

The definition of a trip varies by monitor.Trips are not all the same.

Enabling Criteria

Operating conditionsthat allow a monitor torun

Trip definitions varyby monitor

How does the Monitor know if a componentpasses or fails the test?

The performance of components and systems iscompared to test standards.

Example:

DTC Number : P0117DTC Definition: ECT Sensor Circuit Low VoltageTest Conditions and standards:

• No engine codes already stored in memory• Engine running• PCM detected ECT sensor input of more than 246° F• All conditions met for a least 500 ms

Test standardsfor P0117 or forany other codewill vary bymake, model,year, andpossibly VIN.

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When Monitors Can’t Run

If the conditions aren’t right, will themonitor run anyhow?

Until all the enabling criteria are met, we won’t havea trip. This ensures that monitors run only whenthey are supposed to run.

Trips allow monitors to run by creating the exactconditions (enabling criteria) needed to run the

monitor correctly.

If conditions are not right, the monitor will not run.For example, the PCM may have detected a previ-ously stored DTC. The DTC might indicate thatthere’s separate problem already present that willkeep the monitor from running properly.

A previous DTC may stop a monitor from running.

The chart to the left shows that atrip allows a monitor to test thesystem.

• All trips start with a key-on.• Then the PCM looks to see if allenabling criteria are met.

• DTCs and Pending codes can stopmonitors. The PCM may wait until theDTC is erased before running othermonitors.

• Monitors must run in the correctorder. Monitors running at the sametime may conflict.

• Test results from one monitor may beused by another monitor.

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The Task Manager/ Diagnostic Executive

What a minute. This is a lot of schedulingand information to keep track of. How doesthe PCM do this?

Each OBD II PCM has special software that storestest standards and data, schedules all tests, recordstest data, stores DTCs, and turns the MIL ON andOFF as needed.

This software program is acombination of an accountant

and a traffic cop!

The software must:• Schedule the tests

so they run at theright time

• Grade the tests

• Issue a passing orfailing grade to the compo-

nent that was tested

• Store a DTC and turn on theMIL if the component or system

flunk the test.

GM and Ford refer to our little data manager as theDiagnostic Executive.

Chrysler refers to him as the Task Manager.The next page contains a large chart showing howmany things the Task manager must take intoconsideration when performing the onboard testprocedures known as monitors.

Task Manager-Chrysler

DiagnosticExecutive-GM and Ford

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So Much to Do-So Little Time!

As you can see, this is a pretty busy dude!His job is to make sure:• that all the enabling criteria are met• that the monitors run to completion

If a fault is detected, he stores a code andaccompanying freeze frame.

To keep everythingstraight, he keeps veryaccurate records on anelectronic clipboard

The key to repairingany OBD II vehicle is totake a look at this clipboard!

We do that with ourscan tool—our windowinto the PCM’s clip-board of data.

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Frequently Asked OBD II Questions

Will some scan tools do more than the Generic Tool?

OEM and aftermarket scan tools loaded with enhancedsoftware provide additional data and perform bidirectional teststo help you diagnose both OBD II and non- OBD II (ABS, SIR,etc.) vehicle problems.

Here are some rapid fire OBD II questions and answers:

Q: How do we know if a vehicle has an OBD II emissions problem?A: The MIL will be on and a DTC will be stored in memory. (Multiple DTCs may bestored.)

Q: Can the MIL come on even if the fault in the systemdoesn’t cause a performance problem?A: Yes. The MIL is illuminated for emissions problems, notperformance problems.

Q: Who turns on the MIL?A: The PCM

Q How does the PCM know there is a problem?A: It runs tests called Monitors

Q: When does it run these tests?A: During normal driving, when conditions are just right to runthe test.

Q: How does the PCM know there is a problem?A: It receives information from sensors and performs tests ofits own on actuators to see if they are working properly.

Q: Can we watch the data used to make these decisions?A: We can view data parameters on a scan tool. All OBD II vehicles have serial data, soa scan tool is an essential tool for working on OBD II vehicles.

Q: Are all scan tools created equal?A: No. But there is a minimum standard for OBD II scan tools. It’s referred to as theGeneric scan tool interface.

At a minimum, the Generic OBD II scan tool should allow you to:• Read and erase DTCs• View engine (powertrain) data parameters• View Freeze Frame data• View a list of Monitors indicating which Non-Continuous monitors have run to completion

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Why We Need a Scan Tool

How does the OBD II scan tool connect to the PCMinterface?

All OBD II vehicles have a diagnostic link connector(DLC) that is usually, but not always, located beneath thedash on the driver’s side of the vehicle.

The OBD II scan tool needs no external power source.It receives its power from pin 4 of the DLC and groundsthough pin 16 (occasionally pin 5).

Is there one standard interfacefor all OBD II vehicles?

No.

This is extremelyimportant!

In many vehicles you will find that thetraditional scan tool interface you’veused for years is still available. You mayeven be asked to enter a VIN number (orparts of a VIN number). This is referredto as the OEM interface.

Notice that the OEM menu choice has adropdown list of options that includecommon scan tool functions like retriev-ing codes, recording movies, and bidirec-tional (ATM) tests.

But the same scan tool can access theOBD II interface when the correctsoftware and cable interface are in-stalled. Then it becomes an OBD II scantool displaying OBD II codes and data.

Always connectthrough the OBDII interface onvehicles that haveseparate OEM andOBD II interfacesor you won’t seeDTCs, FreezeFrame, or Monitorstatus.

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Important Diagnostic Information

The Generic OBD II scan tool interface wasdesigned specifically to provide us with usefuldiagnostic information, including any DTCs,Freeze Frame, and Datastream.

Are OBD II DTCs like the OBD I DTCs?

OBD II Diagnostic Trouble Codes arebetter for several reasons:

• There are many more DTCscovering more components andsystems.

• The DTCs are better defined. Inmany instances, the code definitionsare more detailed and specific.

First Digit:P = PowertrainB = BodyC = ChassisU = NetworkCommunications

SecondDigit:

0 = SAE Code

1= OEM Code

Third Digit=AffectedSystem

1 = Air Fuel2 = Fuel System3 = Ignition/ Misfire4 = Auxiliary Emissions

5 = Vehicle speed/idle speed controls

6 = PCM communications7 = Transaxle8 = Transaxle

Actual Code,

In this case 18 stands for:ECT Circuit High Voltage

Quick Tip:You don’t need to memorizethis chart to use DTCs.

Simply look up the DTC in arepair database.

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Diagnostic Trouble Codes

Using DTCs

DTCs are an extremely useful source of diagnosticinformation—if you take the time to look up theirexact definition. Here’s an example.

Start with the DTCNumber. Retrieve DTCsfrom the OBD II interfaceand write them down.

Then look up the DTC Definition in a repairdatabase or reference manual.

Note any CodeSet Conditionsthat are listedwith the DTCDefinition.

These conditionsmay be verysimple or morespecific.

These are theoperatingconditionsneeded for thetest to run.

This informationcan help usduplicate testconditions tocheck forintermittents.

Code Set Criteria are the test standards.

In this case, the PCM has detected that the ECT isregistering a minus 4 degree F coolant temperature in anengine that has been running to 8 minutes! Not likely.

This combination of code set conditions and test standardssuggests a higher than acceptable ECT signal voltage,commonly caused by an open in the ECT circuit.

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Storing DTCs

Are DTCs stored the instant a problemoccurs?

For a DTC to be stored and turn on the MIL, severalthings must happen:

1) The code set condi-tions must be met so thetest can run, and the testresults must fail, accordingto the code set criteria(test standards). That partis similar to what we’ve always seen in vehicleonboard diagnostics.

2) Some codes will turn on the MIL in a single trip.These are called One-Trip Codes.

Some onboard test procedures may not turn on theMIL and store a DTC until a fault is seen on twoconsecutive trips. In some instances it may actuallytake more than two consecutivefailures to turn on theMIL. Toyota has usedtwo-trip fault detectionfor years.

These are calledTwo-Trip Codes.

Code Set Conditions

Conditions needed torun a test

Code Set Criteria

Performancestandards thatdetermine a test’spass-fail status

If the PCM sees first occurrence of a fault that must be seen again onthe next trip to store a DTC, it records a Pending code. Pendingcodes do not turn on the MIL. They are stored when the PCM sees aproblem that will Mature into a full-blown DTC and turn on the MIL ifit is detected again on the next consecutive trip.

Pending codes can be viewed on some scan tool interfaces.

Two Trip Codes

Store a DTC and Turnon the MIL when thefault is detected ontwo consecutive trips.Also known as Type-Bcodes.

One Trip Codes

Store a DTC and Turnon the MIL in a singletrip. Also known asType-A codes.

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How DTCs Turn on the MIL

This chart shows howOBD II stores DTCs andFreeze Frame.

Fuel and Misfire DTCs fallinto a special categorysince either can result incatalytic converter dam-age. In fact, a severemisfire can store a DTC ina single trip, and may evencause the MIL to flash aslong as a catalyst-damag-ing misfire is present.

Most two-trip DTC faultsmust occur on consecu-tive trips to store a DTC.

But once a fuel or misfirefault is detected, anyrepeat of the fault insimilar driving conditionsduring the next 80 tripscan store a DTC.

Freeze Frame is stored withthe first DTC.

Note: A Freeze Frame maybe overwritten by a later DTCfor fuel or misfire.

Caution: If you erase DTCs,you also erase Freeze Frame.

Always record Freeze Framedata before erasing DTCs.

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Erasing DTCs and Turning OFF the MIL

Erasing DTCs

DTCs can be erased by removing power from the PCM until KeepAlive Memory is erased. This is NOT the recommended code erasingprocedure, however.

Instead, it’s better to erase DTCs with a command from your scan tool.That way, you won’t erase all the other controller memories— clock,radio presets, etc. — by disconnecting the battery!

Caution: Erasing DTCs will also erase Freeze Frame, and you’ll losethe diagnostic information contained in the Freeze Frame data list. You’llalso reset any Non-Continuous Monitors to Incomplete.

What does it mean to Reset Monitors to Incomplete?

The OBD II Generic Scan tool interfaceincludes a Readiness Status display.

Readiness Status lists all monitorsinstalled in the vehicle, both Continuousand Non-Continuous.

When the PCM loses power (KAM) orDTCs are erased with a scan tool, allNon-Continuous monitors are reset toan incomplete status. They will continueto be displayed as incomplete until eachone runs again to completion.

Caution:While somescan tools usethe termsIncomplete andComplete toindicate currentmonitor status,some will useterms like YES/NO, or Done/Pending.

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Erasing DTCs and Turning OFF the MIL

Can the PCM turn out the MIL anderase DTCs?

You bet your scan tool!

If the PCM runs the same test thatstored the DTC in the first place—butthe test passes on three consecutivetrips—the PCM turns OFF the MIL...

But the DTCremains in memory

The DTC stays inmemory until the PCMcounts 40 warm-upcycles without a recur-rence of the fault.

Then it will erase theDTC.

This is very importantfrom a diagnostic per-spective.

Just because the MIL isnot ON, does not meanthat there isn’t a DTC inmemory.

Always check for DTCsduring a vehicle diagno-sis, even if the MIL is notpresently lit!

The PCM needs to see a start to run where the enginecoolant temperature increases by at least 40 degrees Fand reaches a temperature greater than 160 degrees Fbefore being shut down.

What does it take for the PCM to count a warm-up?

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Let’s stop here for a quick review beforewe move on to OBD II troubleshooting!

What we know so far:

• OBD II is an onboard monitoring system designedto detect vehicle failures that will result in increased

vehicle emissions.

• The OBD II scan tool interfaces with the PCM at astandardized Diagnostic Link Connector, referred to as the

DLC. The OBD II scan tool is powered through the DLC andrequires no external power supply.

• The OBD II Generic interface allows us to read and erase DTCs. It should alsoallow us to view Freeze Frame, powertrain-related datastream parameters, andMonitor status.

• The OEM and OBD II scan tool interfaces are not the same in most vehicles.Accessing all the repair information available from a vehicle may require separatescan tool interfaces (specialized software and/or cables).

• Monitors test the vehicle. Some Monitors run continuously; others (non-continuous) once per trip.

• All OBD II vehicles have Comprehensive Component, Fuel System, and MisfireMonitors, which are Continuous Monitors.

• Trips are specific modes of vehicle operation that allow monitors to run. Monitorsthat run and fail store DTCs.

• A single frame snapshot of critical vehicle operating parameters known as FreezeFrame is stored with the first, or highest priority, DTC.

• DTCs are best erased with the scan tool. Erasing DTCs also erases Freeze Frameand resets all Non-Continuous Monitors to Incomplete.

• The PCM may turn off the MIL if the test that stored the DTC runs and passes onthree consecutive trips. The PCM may also erase DTCs if the fault is not detectedagain for 40 warm-ups.

• A warm-up is defined as vehicle operation where the engine coolant increases by40 degrees F and exceeds 160 degrees before shutdown.

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You probably know more than you think about OBD II

This section is about OBD II Troubleshooting.

But before we get all ner vous and sweaty abouthaving to learn some newfangled, black box, techno-nightmare, pain in the neck diagnostic system fromscratch, we need to stop for a minute and thinkabout what’s really going on here.

OBD II is not totally new.OBD II is an upgrade of several old

diagnostic strategies.

Here are some examples:

PCM Diagnostic Tests

Onboard diagnostic tests are not new. Ford startedusing self tests to check computer and componentfunctions, even before their vehicles had datastream. Ifyou understand KOEO and KOER tests, you knowthat Ford computers can test the PCM and manyvehicle sensors and actuators.

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Serial DataDomestic vehicles have long used serial data toallow scan tool code and data retrieval.

What’s new is that all OBD II vehicles must havea serial data interface that supports the GenericScan tool interface.

Check Engine Light/MILWe now call it the Malfunction Indicator Light(MIL), but we used to call it the Check Engine orSer vice Engine Soon light.

MIL illumination is reserved for emissions-relatedfaults. Failures in other non-emissions relatedsystems will illuminate separate warning lights(ABS, SIR, etc.)

OEM Powertrain Control SoftwareOBD II doesn’t replace OEM powertrain controlsoftware. Ford still has EEC, Chrysler hasSBEC, and Jeep has JTEC, etc.

Admittedly, OE systems have been modif ied andimproved, but you don’t need to relearn OEMoperating strategies from scratch. Build on whatyou already know and add OBD II!

You Know More Than You Think About OBD II

The Scan Tool InterfaceSimilar to OBD I, but an improvement in that theshape of the scan tool connector (DLC) is standard-ized.

Each DLC has a 16-cavity connector that includespower and ground terminals for the scan tool.Some scan tools need a personality key/ specialcartridge to operate as an OBD II scan tool

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You Know More Than You Think About OBD II

Misfire DetectionMisfire DetectionWhile OBD II misfire detection is more sophisti-cated than any misf ire tests run before, the conceptof misfire monitoring isn’t new.

Ford’s IDM and Toyota’s IGF sensor lines have beenused to monitor ignition coil f iring even before OBDII came along!

Oxygen SensorsOxygen sensors are still the main sensor for closedloop fuel control and Fuel System monitoring, butthey play a larger role in OBD II diagnostics.

Oxygen sensors are now heated to operate withinminutes of a cold engine start-up. They also serve asa sensor input for several monitors, including: Misfire,Catalyst, EVAP, EGR, and AIR.

DatastreamYou are already familiar with datastream from yourexperience with GM, Ford, and Chrysler.

The good news is that generic datastream is nowavailable on all vehicles. This is a big benefit to techsworking on vehicles that had no serial data interfacebefore OBD II.

Trouble CodesYou know code, only there are a lot more codes nowand they are referred to as DTCs (Diagnostic TroubleCodes). Retrieve them with the scan tool.

Each OBD II DTC is 5 digits long. You’re familiar withthe concept of codes, and now you can expect moreinformation from DTCs since they are better definedand have more specific fault descriptions.

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Common SensorsTested by the CCM

• MAF• MAP• BARO• ECT• IAT• VSS• CKP• CMP• CNG Fuel Temp• TP• Battery Temp• P/S Switch• PRNDL• O2S Heater• PCM• Brake Switch• TOT

Common OutputsTested by the CCM

• Fuel Injectors• Ignition Coils• TCC• Transmission shift solenoids• IAC• Purge Solenoid• EVAP Vent Solenoid• EGR Solenoid• Linear EGR• DPFE• Oxygen sensor heaters• Radiator Fan Control

ComComComComComprprprprprehensivehensivehensivehensivehensiveeeee

ComComComComComponentsponentsponentsponentsponents

The Comprehensive Components Monitor (CCM) isthe core of the onboard monitoring operation. It is aContinuous Monitor.

Vehicle operation and emission control starts withthe inputs and outputs monitored by the CCM.

Look to the left column on this page to see com-monly monitored inputs. Now look to the right tosee a similar list of outputs.

You can see why it’s so important for the onboardmonitoring system to verify that the “basics” are allin order, first and foremost.

Failure of any of these core components can affectvehicle operation, increase vehicle emissions, orprevent one or all of the onboard monitors fromrunning.

Since all of these inputs and outputs aretested by the PCM, using a scan tool to viewdatastream becomes an essential part of anydiagnosis and repair.

We’ve mentioned monitors repeatedly. Over the next few pages, we’lltake them in order and outline their major features to give you abetter feel for how they fit into the overall OBD II monitoring strategy.

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ComComComComComprprprprprehensivehensivehensivehensivehensiveeeee

ComComComComComponentsponentsponentsponentsponents

What areComprehensiveComponents?

Switches, sensors,motors, solenoids, etc.

What are they testedfor?

All components testedby the CCM mustpass basic circuit teststo determine if theyare shorted or open.

They may also betested forfunctionality, toensure that theyrespond to commandsfrom the PCM.

Rationality testscompare sensorinputs to see if thesignals sent to thePCM are rational(make sense) whencompared to oneanother.

MAF and MAP

VacuumSolenoids

Speed Sensors

TemperatureSensors

When are they tested?

Many CCM tests are run as soon as theignition is switched on to detect shorts andopens.

Additional functionality and rationality testsmay be performed during normal KOERoperation.

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How Does the Misfire Monitor Work?

The misfire monitor watches the crankshaft sensor,looking for changes in crankshaft speed that wouldindicate a misfire condition.

This works because the crankshaft slows slightlyeach time a misfire occurs. Sticking driveline compo-nents or rough roads can also slow the crankshaft,so the PCM may use special filtering software toscreen out false signals or it may rely on wheel speedsensors to detect rough roads.

Common Causes forMisfire DTCs

• Worn spark plugs• Cracked distributor caps• Out of Phase distributor/rotor• Shorted rotors• Leaking plug wires• Low fuel pressure• Low compression• Sticking valves• Broken valve springs• Worn cam lobes• Incorrect valve or ignition timing• Leaking EGR• Vacuum leaks• Leaking Injectors• Clogged Injectors• Contaminated fuel• Low fuel tank level• Excessive EVAP purge• Low ignition system primary voltage• Cracked coils• Plugged exhaust• Excessive PCV flow• Wiring Harness• Faulty PCM

Full Range Misfire

Early OBD II vehiclesdid not detect misfireat all engine speeds.

Newer misfiremonitors detectmisfire at all RPM andare referred to as FullRange Misfiresystems.

MisfMisfMisfMisfMisfiririririreeeee

MonitMonitMonitMonitMonitororororor

We commonly think of spark plugs and plug wireswhen we think of misfire. Use traditional engineanalyzer/power balance tests, vacuum and fuelpressure readings to isolate and correct misfireconditions.

Don’t forget all the items listed in the “CommonCause for Misfire” list on this page, especially whentroubleshooting those tough misfire problems.Anything that prevents combustion causes misfire.

In some instances, reprogramming the PCM toinstall revised software may be the only way to curesome misfire codes.

Adaptive Numerator

The PCM must “learn”the crankshaft beforethe misfire monitor willrun. “Learning” thecrankshaft allows thePCM to makeallowances for slightvariations in machiningand sensor tolerancesthat might set falsecodes.

Procedures vary bymanufacturer.

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MisfMisfMisfMisfMisfiririririreeeee


Sensor Inputs:

Engine SpeedSensor

May also look atadditional sensors likethe O2S and wheelspeed sensors toverify existence of truecylinder misfire

Misfire DTCs:

P0300 Series Codes

Individual cylindermisfire may beidentified by last twodigits of code.

Example: P0305indicates misfire oncylinder number 5.

Monitor Disablers

The misfire monitor may not run under someconditions, including:• Fuel tank level above 85% or below 15%• Rough road conditions• Rapid TP voltage fluctuations• Engine RPM out of range (some)• PCM has not learned crankshaft characteristics

Misfire Monitormay flash the MIL toindicate severe(catalyst damaging)misfire levels.

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FFFFFuel Syuel Syuel Syuel Syuel Syssssstttttememememem


What are Fuel Trim

Numbers?

The PCM keeprunning records of theamount of fuelcorrection it needs tomake to maintain thecorrect air/fuelbalance in closedloop.

The amount of fuelthat must be added orsubtracted to keepthe system inclosed loop isknown as ShortTerm Fuel Trim(STFT).

The average ofSTFT correctionsover time is calledLong Term FuelCorrection (LTFT).

LTFT indicates longterm trends in fuelcorrection.

How Do We InterpretFuel Trim Numbers?

STFT and LTFT aredisplayed on a scantool as numbers from0 to 255 in GMvehicles, with 128being the center.

• At 128, fuel is neitheradded or subtracted.

• Numbers lower than128 indicate that fuelis being subtracted.

• Numbers greaterthan 128 indicate thatfuel is being added.

How does OBD IIdisplay fuelcorrection indatastream?

OBD II generic datawill display STFT andLTFT a little differently—as a percentagechange from zero.

Positive percentagesmean fuel is beingadded.

Negativepercentages indicatethat fuel is beingsubtracted tocompensate for analready rich condition.

What does Short Term Fuel Trim do?

It maintains the best fuel air ratio in closedloop. This adjustment changes constantly in re-sponse to oxygen sensor inputs.

How does the PCM adjust fuel delivery?

By adjusting injectorpulse width.• When the PCMdetects a leanmixture, it leavesthe injectors onlonger todelivermorefuel.

• When thePCM detects a rich

mixture, it reducesinjector on-time to take

away fuel.

We can watch these continual corrections onthe scan tool STFT data parameter, or PID. LTFTwill also shift richer or leaner, based on averageSTFT corrections.

Here’s where the DTC is stored: When acombination of STFT and LTFT are greater thanthe test limit, a DTC is stored to tell us that thesystem is far to rich, or far too lean.

The DTC tells us that the PCM can no longer controlthe fuel ratio by adjusting pulse width. Something isdriving the system so lean—or so rich-that the PCMcan’t correct the situation. That “something” is whatwe need to fix!

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FFFFFuel Syuel Syuel Syuel Syuel Syssssstttttememememem


Common Enabling Conditions for the FuelSystem Monitor:

• PCM in closed loop fuel control• Fuel tank above 15% and below 85% of capacity

What can cause afuel system DTC?

Anything that makes itimpossible for thePCM to maintain thecorrect air fuel ratio.

For example, FuelSystem Lean DTCscan be caused bythings like:

• A weak fuel pump• Fuel pump low voltage• A plugged fuel filter• Restricted fuel supply hose• Clogged injectors• Faulty MAF• Faulty MAP• Faulty Fuel Pressure regulator

Fuel System RichDTCs may be causedby things like:

• Excessive fuel pressure• Leaking injectors• Excessive injector pulse width

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So far, we’ve discussed the three Continuous Moni-tors that can be found in all OBD II vehicles:

• Continuous Component• Fuel System• Misfire

Now, it’s time to look at the Non-Continuous Moni-tors is a little more detail. Non-Continuous Monitorstest subsystems that are designed to control vehicleemissions, and include:

• Oxygen Sensor Monitor• Catalyst Monitor• EGR Monitor• EVAP• AIR Monitor• PCV Monitor• Thermostat Monitor

Which Vehicles Use WhichMonitors?

All OBD II vehicles use the samethree Continuous Monitors. Non-Continuous Monitor use varies byvehicle.

For example, a manufacturer may notequip their vehicles with air injection,so the AIR monitor won’t be used.

To find out which Non-Continuousmonitors are installed in a vehicle,connect your scan tool and navigateto the Readiness Status display thatwill list installed monitors.

NNNNNon-Continuous Moniton-Continuous Moniton-Continuous Moniton-Continuous Moniton-Continuous Monitorororororsssss

Additional Monitors

There are twoadditional monitors wewon’t discuss in detail.

• The A/C RefrigerantMonitor which wasintended to monitor R-12 systems for leaks.R-12 is out ofproduction.

• The HeatedCatalyst Monitor issupposed to testcatalyst mountedelectrical heatersused to bring thecatalyst to operatingtemperature faster.

We may see thismonitor in regular useafter vehicles changeover to 42 voltsystems that canprovide the massiveamounts of currentthese heaters willconsume.

Commonabbreviations:O2S = Oxygen sensorHO2S = HeatedOxygen Sensor

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OxyOxyOxyOxyOxygggggenenenenen

SensorSensorSensorSensorSensor


Non-Continuous Monitors

CatCatCatCatCatalalalalalyyyyyssssst Eft Eft Eft Eft Efffffficiencyiciencyiciencyiciencyiciency


The oxygen sensor monitor “measures” oxygensensor performance in several ways. This chartshows that a good oxygen sensor ought to reachcertain minimum and maximum voltage levels andcross rich and lean thresholds. It ought to switchfrom rich-lean to lean-rich rapidly.

All in all, the sensor is tested for voltage range,reflexes, and time to respond to changes in exhaustgas oxygen content.

The Oxygen Sensormonitor tests bothupstream sensors(ahead of the catalyst)and downstreamsensors (after thecatalyst).

Important: A DTC forthe oxygen sensorscan prevent severalother monitors fromrunning.

Oxygen sensors don’tjust work with fuelcontrol. They are alsoused as test inputs forthe Misfire, EVAP,EGR, CatalystEfficiency, and AIRmonitors.

• This is a Non-Continuous Monitor

• The CatalystMonitor depends onup and downstreamoxygen sensoraccuracy

The Catalyst EfficiencyMonitor is one of the morecomplex OBD II test strate-gies.

The catalyst test comparesthe upstream and down-stream oxygen sensorvoltage signals. If the catalyst is able to store and use oxygen, the downstreamsensor voltage will stay relatively flat. If catalyst oxygen storage efficiency falls,however, the downstream signal will begin to mimic that of the upstream sensor,indicating reduced catalyst eff iciency.

The PCM may run additional tests and perform some complicated math beforeultimately condemning the catalyst and storing a DTC.

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AIR MonitAIR MonitAIR MonitAIR MonitAIR Monitororororor

EGR MonitEGR MonitEGR MonitEGR MonitEGR MonitorororororOBD II tests EGR valve operation. It also tests forsufficient exhaust gas flow into the intake mani-fold.

EGR is one area where the OEMs differ onhow to best operate and monitor exhaust gasrecirculation.

Ford uses a Differential Pressure EGR thatsenses pressure changes in the manifold as theEGR valve opens.

GM uses a motor-activated EGR with integralposition sensor, called a Liner EGR valve. TheGM PCM measures changes in manifold pres-sure to determine exhaust gas flow rates.

Chrysler uses both a Linear EGR similar toGM’s and a more traditional backpressuretransducer EGR setup. Chrysler checks EGR flowrates in speed density systems with the oxygensensor by measuring the change in exhaust gasoxygen content as the EGR opens.

An air pump is used in some makes to send additional air into the exhaust to help oxidize unburned fuel.

The AIR Monitor watches oxygen sensorvoltage during warm-up, before the systementers closed loop. If the AIR system ispumping air into the exhaust as it should,the added oxygen will drive the O2 sensorvoltage low.

If this test is inconclusive, the pump may beturned on again briefly after closed loopstarts. Once again, the PCM will look for achange in O2 sensor voltage to indicate airinjection is working.

This graphic shows a belt-drivenair pump, although most pumpsare electrically operated now.


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EVEVEVEVEVAP MonitAP MonitAP MonitAP MonitAP Monitororororor

Of all the monitors, Misfire and Enhanced EVAPseem to cause the most aggravation for repairtechnicians. Misfire is tough because there are somany causes for a misfire to occur.

Enhanced EVAP is just as tough for dif ferent rea-sons. EVAP must:• Test for proper purge flow.• Detect fuel vapor leaks as small as 0.20 inch.

This is a tough monitor for the PCM to run, since itmust compensate for rapid fluctuations in fuel tankpressure caused by changes in ambient tempera-ture, barometric pressure, fuel sloshing aroundinside the tank, and the effects of hot fuel returningto the tank from the fuel rail.

• The PCM looks atchanges in STFT asthe Purge Solenoidis opened to mea-sure fuel vapor purgeflow rates.

• EVAP leak testsare different. Acombination ofvacuum switchingvalves and ventsolenoids seal offparts of the systemas a fuel tank pres-sure sensor monitorstank pressure andvacuum.

Before OBD, II we hadnon-enhanced EVAP.The onboard systemtested for EVAP purgevalve operation, butdidn’t really test forvapor leaks in the fuelvapor containmentsystem (canister, fueltank, connectinghoses, etc.).

Enhanced EVAP alsotests for leaks in thevapor containmentsystem.

Most of us are used tomeasuring pressure inpounds-per-squareinch. EVAP systemvapor pressures aremeasured in inches-of-water.

A false leak may becaused by somethingas simple as a loosefuel filler cap.


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PCV MonitPCV MonitPCV MonitPCV MonitPCV Monitororororor

TherTherTherTherThermosmosmosmosmostttttat Monitat Monitat Monitat Monitat MonitorororororThis monitor is being phased in beginning with 2000 M/Y. Its purpose isto ensure that the engine coolant temperature reaches normal operatingtemperature within a specif ied time after start-up. This function waspreviously a part of the ECT test.

Here’s an example of a DTC for improper warm-up:

P0118 ECT Sensor Circuit Low Temperature• Code Set Conditions: Engine run time over 4 minutes• Code Set Criteria: PCM detects ECT sensor input below -31 degrees F for 5 seconds

Brand new for 2002, this monitor will also be phased into production.The purpose of this monitor is to detect PCV leaks, either at the PCVvalve itself, or at the engine vacuum connection.


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OBD Tool Box

What tools do you need in order to repair OBD IIvehicles? While the possible list is as long as ourimagination, we want to give you a core list of toolswe feel are essential for successful OBD II repairs.

Number ONE - Scan Tool

A scan tool. There’s only one way to retrieve DTCsand Freeze Frame and view datastream and MonitorReadiness informationand that’s with a scantool.

Earlier, we suggestedthat the Task Managerwrites down test dataand test results on anelectronic clipboardlocated inside the PCM.

The only way to viewthe contents of thatclipboard is to peekover the TaskManager’s shoulderand look at contents ofthat clipboard.

The scan tool is yourwindow into the work-ings of the Task Man-ager and the OBDDiagnostic System.

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Number Two: Information

We can’t fix the car until we know exactly why itfailed. We’ve shown you that test enabling criteriaand test standards are very specific. They oftenvary by make, model, year, and even VIN.

You need access to repair data, including Techni-cal Service bulletins that list changes in hardware,software, and adjustment procedures.

Number Three: A Good DVOM

Many DTCs are caused by shorts and opens incircuits and sensors. For quick tests of availablevoltage and voltage drops, there’s no substitute fora quality DVOM.

Tip: Use the MIN/MAX and Alert functions onyour meter to record intermittents.Tip: Add a low amp probe and test circuits forcorrect current while they work.

OBD II Troubleshooting Tools and Equipment

Number Three: A Labscope

Number Four: An Engine Analyzer

An engine analyzer benefits diagnosis ofmultiple problems because it let’s you look atwhat’s happening inside the cylinder.

Misf ire, fuel delivery, ignition and valve timing,and engine mechanical problems will all showup on scope primary and secondary patterns.

As useful as a DVOM can be for basic voltage andresistance tests, it can’t identify certain problemswith repetitive waveforms used to signal speed andduty cycle.

A picture is still worth a thousand words.

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OBD II Troubleshooting Tools and Equipment

Number Six: A Fuel Pressure Gauge

One of the most overlooked (and common) rea-sons for Fuel System codes is low fuel pressureand insufficient fuel volume.

Once you’ve identified a rich or lean condition in avehicle, fuel pressure and fuel volume tests be-come logical and essential parts of a completediagnosis.

Number Seven: A Smoke Machine

Smoke machines are great for locating intakemanifold and exhaust system leaks.

Many techs have also found them a more user-friendly alternative to ultrasonic leak detectorsfor locating EVAP leaks.

Leaks may seem low tech, but they cause a lot ofproblems.

Number Eight: A Vacuum Gauge

Low tech and inexpensive, the lowly vacuumgauge is still one of the fastest and mosteffective ways to diagnose common enginemechanical and exhaust backpressure prob-lems in a running engine.

Also helpful for identifying engine crankingvacuum problems.

This is the short list. You have items you’d like to add. But the toolsand equipment listed on this page should be considered essential,core testers for diagnosing OBD II problems.

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TTTTTypical Diagnosypical Diagnosypical Diagnosypical Diagnosypical Diagnostic Stic Stic Stic Stic Stttttepsepsepsepseps

1) It is our considered opinion that for themajority of OBD II concerns, the scan tooland accurate vehicle information areyour two most important diagnostic tools.

2) Read Statement 1 again as many times asit takes to remember it.

Now we can move on.

Before we start the test section, we want tomake two simple statements:

Let’s run through a generic OBD IIdiagnostic procedure. The MIL is ON!

1) Connect your scan tool and retrieve all DTCs

2) Look up the exact DTC definition, including testenabling criteria and code set standards.

3) View Freeze Frame. Look for clues in Freeze Freezethat match the code definition and/or symptom.

4) If the DTC in memory is for a component failure thatinvolves a short or open circuit, locate that componentin datastream on the scan tool and view its currentvalue. If the PID indicates that a short or open is stillpresent (hard fault), use a wiring diagram, voltmeter,etc. to locate and correct the fault.

Component DTCs must be repaired first!

Typical Diagnostic Steps

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7) Use Freeze Frame to determine thevehicle operating conditions that werepresent when the DTC was stored. Dupli-cate those conditions on a test drive withyour scanner taking a datastream movie.

This is a great way to catch intermittentproblems in the act or to view trends that canlead to a DTC down the road.

5) Compare datastream toFreeze Frame PIDs. Look fordata that “matches up” withthe DTC definition.

If your scan tool supports agraphing mode, use it to lookfor dropouts and glitches.

Select PIDs that match thecomponent or system thatstored the DTC.

Example: make sure youselect the ECT PID for anECT code.

Don’t select too manyPIDs at once inGeneric OBD II.

Doing so may slow thescanner’s update ratesignificantly.

Limit selected PIDs toabout 4 to get thefastest update.

Note: Newer Genericinterfaces haveimproved serial datatransfer rates.

Experiment to get thefastest updates.

6) Look very carefully at Freeze Frame. FF issupposed to help with a diagnosis.

The Freeze Frame to the right is an example,taken from a case study. The DTC is for amisfire, but Freeze Frame indicates anextremely lean mixture (the PCM is adding 36-38% to the pulse width long term).

The problem? Lean misfire caused by a weakfuel pump.

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8) Use your scan tool in Actuator Testor Output State test mode to activatesuspect components.

Then use your DVOM, labscope, lowamp probe, fuel gauge, etc. to verifycomponent operation.

Compare your meter/gauge readings tothe data shown on your scan tool.


Do NOT Erase DTCs until you record Freeze Frame data.Erasing DTCs erases Freeze Frame.

9) GM vehicles will display both Current and HistoryMisfire data. Compare the two to identify anintermittent misfire condition.

Then use Freeze Frame, either to duplicate thoseconditions, or to determine which components mightcause misfire under similar conditions.

10) Familiarize yourself withspecial scan tool test modes thatcan speed diagnosis.

You can still access KOEO andKOER tests on EEC-V OBD IIFords, but you have to do itthrough the scan tool now.

Don’t forget Wiggle Tests. Theyare very useful for locatingintermittent conditions.

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11) Fix the car. At this point, we revert to the same standard repair practiceswe’ve used for years. In many cases, the problem that stores a DTC will not beany different from similar problems we’ve diagnosed and repaired in the past:misfires, short circuits, open circuits, fuel starvation, excessive EGR, etc.

When you erase DTCs following repairs, the onboard system will run itsmonitors again to test your work, and store fresh DTCs, if necessary.


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OBD II is a software-driven troubleshooting machine that monitors, measures, and evaluatesvehicle data provided by various sensors to locate, label, and identify vehicle faults that result inincreased emissions.

Monitors check vehicle components andsystems during normal driving.

Some monitors run Continuously: othersare Non-continuous. The PCM monitorsdatastream looking for problems that

indicate emission-related vehicle failures.

Trips are specific driving conditions that let themonitors run. Trips definitions vary by monitor.

The PCM stores a (DTC) andturns on the MIL to alert thedriver when a monitor fails.

A skilled Auto Repair Technician must climb back up the steps thatstored the DTC in the first place. OBD II repairs are a logical, step-by-step procedure that results in an effective repair.

• Retrieve DTCs and view Freeze Frame with thescan tool.

• Look for data parametersthat indicate a problem

Attempt to duplicatevehicle operatingconditions that werepresent when the DTCwas stored

After repairs, thevehicle will testitself by runningits monitors.

• Study Freeze Frame. Look for data cluesabout the exact nature of the failure

• Look up the exact DTC definition, code testand code set criteria.

A Freeze Framesnapshot of criticalengine parametersis saved with thefirst DTC stored.

• View/study datastream


Vehicle problems are funneled into the OBD IIsoftware to store DTCs and Freeze Frame.

Our task is to climb back through the steps thatstored the code to diagnose and repair thevehicle.

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What are Modes?

SAE paper J1979describes the diag-nostic test modesnecessary to meetCARB and FederalOBD standards for anOBD II scan toolinterface.

J1979 lists eightmodes of scan tooloperation.

The eight modes arelisted to the right.

Note that the number-ing system includes adollar sign ($).

For example:Mode $01= Mode 1,Mode $02= Mode 2,and so forth.

You are familiarwith many of thesemodes already anduse them regularly.

Modes 1-4 are themost familiar, sincethey allow us toview datastreamand review anderase DTCs.

Advanced Troubleshooting with Test Mode 6

• Mode $01 - Request Current Powertrain Diagnostic Data (what we normally refer to as datastream)• Mode $02 - Request Freeze Frame Data• Mode $03 - Request DTCs• Mode $04 - Clear/Reset DTCs, Freeze Frame, and reset Readi-

ness Status for non-continuous monitors to INCOMPLETE• Mode $05 - Request Oxygen Sensor Monitor test results

• Mode $06 - Request onboard monitoringtest results for non-continuously moni-tored systems

• Mode $07 - Request onboard monitoring test results for con-tinuously monitored systems

• Mode $08 - Request control of onboard system

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You may already be familiar with advantages of Mode 6 ifyou’re using Failure Records to diagnose GM vehicles.

That’s right, Mode 6 has been with us all along in theGM scan tool interface.

GM’s DiagnosticTest Status scan-ner display tells ushow well the non-continuous moni-tors are doing withtheir tests.

We don’t have towait for a pendingcode or DTC to bestored to know ifwe have a problemwith a non-continuouslymonitoredcomponent orsystem.

We can simply goto the DiagnosticTest Statusdisplay in a GMscan interface andview the non-continuousmonitor reportcards.

Notice that one column of thereport card display tells us if thetest for a given monitor has run— or if it hasn’t run.

If the test has run successfullyand gotten a passing grade, it ismarked as a “pass.” If it runs, but doesn’t get apassing grade, it’s marked as a “fail.”

Finally, if the results of the test are inconclusiveor questionable, the test gets an INT grade,indicating a questionable test condition thatmay be intermittent in nature.

Now you see whyit’s sometimesimportant to knowthe conditionsneeded to run amonitor.

If we don’t get themonitor to run, itwon’t perform thetest and we’ll get a“NO” indication inthe “RUN” column.

Mode Six In GM

A failing grade can alert us to acondition that will store a DTC if itisn’t corrected. This is a good wayto confirm the success of a repairwithout driving the car until a codeis stored and the MIL illuminates.

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Mode Six In Generic OBD II

Viewing Mode 6 information

Not all scan tools will display Mode 6information. Sorry about that.

Mastertech is one scan tool that will give usMode 6 test data. Notice that the letters andnumbers in the scan tool display are a littledifferent from what we’re used to seeing.More of those dollar signs!

Don’t let those dollar signs annoy you.TID simply stands for a Test ID for a givenmonitor. Each Test ID (TID) is identified byits own number, such as $01 or $02.

The same thing applies to any ComponentIDs (CID) related to that test. This isespecially important when a test of a systemincludes individual tests of multiplecomponents.

A CID is just a manufacturer-definedcomponent or test status identifier thathelps you identify certain parts of testprocedures.

Once we identify a Test and /or Component,we can simply look in this display window tosee if it has passed or failed a test. This cangive us an early warning about whether ornot a monitor is likely to store a DTC.

TID = Test IDCID = Component ID

How do we read this secret TID and CID code?

Some manufacturers have published TID andCID identifications, allowing us to match teststo monitors and perform Mode 6 diagnosis.Toyota and Ford have published this data onthe web at i-ATN.

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Mode Six In Generic OBD IIHere’s a screencapture from a FordExplorer displayed byEASE diagnosticsoftware, a PC-basedscan tool that canalso display Mode 6test results.

Note: We hadalready pulled aPending CodeP0401 for EGRinsufficient flow.

Armed with thePending DTC andMode 6, we cantackle this problem.

First, refer to the twotests shown in thedisplay to the right.

Note that of the twotests, one is a FAIL.

• The Ford pages on the i-ATN (iatn.net) tell us that the TID and CIDvalues shown in our test screen apply to the DPFE (DifferentialPressure Feedback EGR). This is also referred to as the DeltaPressure Feedback EGR.

TIC CID Chart Ford DPFE

TTTTTest IDest IDest IDest IDest ID Comp ID DescriptionComp ID DescriptionComp ID DescriptionComp ID DescriptionComp ID Description Units Units Units Units Units

$41$41$41$41$41 $11 Delta Pressure for upstream hose test in. H$11 Delta Pressure for upstream hose test in. H$11 Delta Pressure for upstream hose test in. H$11 Delta Pressure for upstream hose test in. H$11 Delta Pressure for upstream hose test in. H2222200000 and threshold and threshold and threshold and threshold and threshold

$41$41$41$41$41 $12 Delta Pressure for downstream hose test in. H$12 Delta Pressure for downstream hose test in. H$12 Delta Pressure for downstream hose test in. H$12 Delta Pressure for downstream hose test in. H$12 Delta Pressure for downstream hose test in. H2222200000 and threshold and threshold and threshold and threshold and threshold

$42$42$42$42$42 $12 Delta Pressure for downstream hose test in. H$12 Delta Pressure for downstream hose test in. H$12 Delta Pressure for downstream hose test in. H$12 Delta Pressure for downstream hose test in. H$12 Delta Pressure for downstream hose test in. H2222200000 and threshold and threshold and threshold and threshold and threshold

Next, we go to the Ford section on the i-ATN (www.i-ATN.net) and look up the test standardsfor the EGR system. The chart below lists the tests run by Ford. Notice that the TID and CIDin the grayed-out box match the ones for the failed test in the EASE screen (TID$41 andCID$12).

We seem to be looking for a problem affecting the downstream DPFE hose. Note that the testspec is a pressure measurement (in H20). We have a pressure problem in the EGR.

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Closer examination of the EGR hoses shows us that the heat-hardened downstream DPFEhose is indeed cracked and leaking. We repair the hose and return to Mode 6 to verify therepair. The Mode 6 screen verifies that the EGR test is now passing. We have aconfirmation that the repair we made was the correct one without having to drive the vehicleon two trips to store a DTC.

Mode Six In Generic OBD II

Things to consider about Mode 6

• Mode 6 is available through the GENERIC OBD II interface on scan tools that support it!You DO NOT need a factory level scan tool, just a generic scan tool that can access Mode6, and trust us, they can’t all do it!

• Even though our Ford test vehicle didn’t store a manufacturer-specific code, Mode 6helped us zero in on the area where the problem occurred (the cracked downstream DPFEhose). Admittedly, there are Ford-specific DTCs, but we didn’t need them here because wehad access to 1) the Pending Code, 2) Mode 6 test results, and 3) Mode 6 definitions,available from the i-ATN for Ford and Toyota.

We suspect that Mode 6 test data for other makes will be more readily available in the nearfuture. In the meantime, we suggest you visit the i-ATN and look more closely at the OEdata for Ford and Toyota. Both manufacturers deserve credit for posting this information.

Mode 6 Screen after Repair

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Ford

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Ford

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Silver Bullets

Ford

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General Motors

Silver Bullets

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General Motors

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Imports

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Silver Bullets

Imports

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Chrysler/Jeep

Imports

Silver Bullets

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Chrysler/Jeep

Silver Bullets

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Adaptive MemoryAdaptive memory is a long term data record of PCM control over adaptivesystem strategies used to maintain fuel control and adapt for vehicle wear andtear. This data is stored in Keep Alive Memory (KAM) and is not erased whenthe ignition is switched off.

AIR (Air Injection) systemThe AIR system injects atmospheric air into the exhaust.

AlphanumericThe OBD II trouble code numbering system is alphanumeric since it mixesnumbers and letters of the alphabet.

Ambient Temperature or PressureAmbient refers to the air surrounding the vehicle. IAT measure ambient airtemperature. BARO measures ambient atmospheric pressure.

BidirectionalA diagnostic interface that allows the PCM and scan tool to both receive andtransmit data.

CatalystA catalytic converter promotes a chemical action to clean exhaust gases.

Comprehensive Component Monitor (CCM)The CCM tests inputs and outputs for functionality and rationality.

ConflictA condition where the OBD II software can’t run a monitor because anothermonitor is already running.

Continuous MonitorA Continuous Monitor runs continuously during normal driving conditions.

Diagnostic ExecutiveThis is the term used by GM and Ford to indicate the PCM software thatschedules tests, stores test data, records DTCs, and turns the MIL on and off.Chrysler calls this the Task Manager.

DLCData Link Connector. This is the standard 16-pin scan tool test connectionmandated for all OBD II vehicles.

GlossarGlossarGlossarGlossarGlossaryyyyy

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DPFEFord’s Differential Pressure Feedback EGR (DPFE) system measures EGR flowrates and sends a variable voltage to the PCM.

DTCDiagnostic Trouble Code

ECTEngine Coolant Temperature sensor

Enabling CriteriaThe exact test conditions required by the OEM to run a diagnostic test.

Enhanced EVAPA diagnostic monitor that tests for both EVAP purge flow and also for EVAPsystem leaks.

EVAPThe Evaporative Emission system

Full-Range Misfire DetectionA misfire monitor that runs at any engine speed.

Functionality TestFunctionality Tests detect clear cut failures of sensors or actuators that canresult in increased emissions.

Freeze FrameA single-frame snapshot engine PIDs stored with the first, or highest priorityDTC, You’ll get at least one Freeze Frame, although some systems can storemore than one of these snapshots.FTPThe Federal Test Procedure (FTP) is a test procedure that sets the baseline fora vehicle’s acceptable emission levels. It includes tests for both tailpipe andevaporative emissions.

HCHydrocarbons


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IACIdle Air Control motor

IATIntake Air Temperature sensor

Inches of WaterOne PSI is equal to 27.68 inches of water. This measurement standard iscommonly used with EVAP system tests.

KAMThe long term data storage area of the PCM that is not erased each time theignition is switched off.

LTFTLong Term Fuel Trim (LTFT) is a record of fuel correction stored in the PCM toindicate long term trends in fuel correction.

MAFMass Air Flow sensors measure the mass of the air being drawn into theengine.

MAPManifold Absolute Pressure is the difference between atmospheric pressure(BARO) and the pressure/vacuum inside the intake manifold. M AP is alsoused as a shorthand reference for the MAP sensor.

MAP SensorThe MAP sensor is used to measure intake manifold pressure as an indicationof engine load based on manifold pressure.

MILThe Malfunction Indicator Lamp.

MisfireAnything that prevents complete combustion.

MonitorThe OBD II term for the test sequence used to check components and systems.


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Non-Enhanced EVAPA system that tests purge flow but doesn’t test for EVAP system fuel vaporleaks.

OBD IOn-board Diagnostics, Generation One.

OBD IIOn-board Diagnostics, Generation Two. This on-board diagnostic system hasbeen standard on passenger cars and light trucks sold in the U.S. since 1996,although there were a limited number of vehicles with some form of OBD II asearly as 1994. OBD II tests for conditions that may lead to unacceptable vehicleemission levels.

OEMOriginal Equipment Manufacturers. For our purposes here, the vehicle manufac-turers.

Oxygen SensorA sensor used to measure the oxygen content in the exhaust. The signal fromthis sensor is used to control closed loop fuel correction and to perform adiagnostic function for several vehicle subsystems.

Oxygen Sensor HeatersA resistance heaters that keeps an oxygen sensor at operating temperatureregardless of exhaust temperature.

Pending CodeThe first detection of a problem that may eventually mature into a DTC. Somefaults must be detected by the PCM on two consecutive trips to store a DTC. APending DTC in the PCM memory indicates that something has failed once.Think of it as strike one!

PCMPowertrain Control Module

PIDOne item in scan tool datastream.


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Readiness StatusA scan tool menu that lists all monitors in a vehicle and indicates whether or notthey have run to completion. If any fails, there should be a DTC stored.

Serial DataData that is transferred by voltage pulses.

Short Term Fuel Trim (STFT)This is the fuel correction needed to keep the engine running in closed loop.STFT is reset each time the ignition is switched off.

Task ManagerChrysler’s term for the Diagnostic Executive.

TripA key cycle (Key-ON, start to-run, and Key-OFF) where driving conditionssatisfy enabling criteria so a monitor can run.

Update RateThis indicates how fast scan tool data is updated

VSSVehicle Speed Sensor

Warm-Up CycleThe PCM may erase DTCs. The PCM can turn off the MIL if the monitor thatoriginally stored the DTC runs again and passes on three consecutive trips. Butthe DTC won’t be erased right away, even though the MIL is off. The DTC caneventually be erased by the PCM if it counts 40 warm-up cycles without seeingany recurrence of the problem. A warm-up cycle is a start-to-run where ECTbegins below 160 degrees F and then increases above 160 degrees F. For awarm up to be counted, however, the ECT must also increase by at least 40degrees.


OBD II Quick Overview - Gem State Gymnastics Academy forro...(ignition coils, solenoids, fuel...

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