New Emissions Book 7-28

8/13/2019 New Emissions Book 7-28

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The AuToEmissions Bible

How to Pass the Vehicle Emissions Test

by Sam Bell

Ralph Birnbaum


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The Auto Emissions Bible

2011 by Sam Bell and Ralph BirnbaumCrooked River Publications

90 Ridge Side Court

330.689.0532Munroe Falls, OH 44262

Cover Design: Ralph Birnbaum

Typeset, Illustrations, and Layout: Ralph Birnbaum

Notice of rightsAll rights reserved. No part of this book may be reproduced or transmitted in any form or by any means, electronic,

mechanical, photocopying, recording, or otherwise, without the prior written permission of the author.

Notice of liability

The information in this book is distributed on an as is basis, without warranty. While every precaution has beentaken in the preparation of this book, the author makes no warranty, express or implied, and will not be liable for

any errors or for incidental or consequential damages resulting from the use of information, herein. Users encour-aged by this book to engage in repair and diagnosis of real vehicles, do so entirely at their own volition and risk.

ISBN: 0-

Hard copies of this book are printed and bound in the United States of America.

Table

of Contents

6

24

40

52

60

81

Combustion

Emission Control Devices

Emission Tests

Analyzing Test Results

Troubleshooting & Tips

Index


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The Auto Emissions Bible6 7The Auto Emissions Bible

Glossary

Air Flow Metering -A fuel control program that determines the amountof fuel needed for combustion by measuring the volume or the mass of airdrawn into the engine.

Closed Loop -A fuel control strategy in which the amount of fuel injectedis continually adjusted to produce an air/fuel mixture that hovers near a stoi-chiometric balance. Te system is referred to as "closed" because the PCM'sfuel adjustments are based in part on a feedback signal from an oxygen sen-sor in the exhaust stream.

DLC(Diagnostic Link Connector) - A 16-pin OBD-II scan tool connec-tor.

Fuel Trim -A scan data value that tells us how far fuel control varies fromthe ideal default value originally programmed into the PCM. Fuel trim isusually divided between long-termand short-termcorrections, referredto as LF and SF, respectively. o find total fuel trim, add LF +SF.

Lambda - Lambda is a value that indicates how close the air/fuel ratio is to14.7:1. At lambda = 1.00, the mixture is in stoichiometric balance. Numbersgreater than 1 indicate a leaner mixture; those smaller than 1 indicate aricher condition. Lambda is not changed by the effects of combustion, oreven by a lack of combustion.

MAP(Manifold Absolute Pressure) = BARO (barometric pressure) minusManifold Vacuum.

Oxidation- Te chemical process of adding oxygen to a compound. Fast

oxidation is called burning.

Reduction- Te opposite of oxidation. Reduction removes oxygen from acompound.

Speed Density - A fuel control strategy based primarily on engine speedand engine load, indicated by changes in manifold absolute pressure (MAP).

Stoichiometry- Te conditions under which a particular chemical reactionproceeds most efficiently. For gasoline engines, stoichiometry occurs at anair/fuel ratio of 14.7 to 1, by weight.

Overview or Just-in-Time ReferenceYou Decide

oo much to read; too little time? Use this book one of two ways:

If youre an auto repair novice, use this as a course book: start at thebeginning and read straight through.

If you already have a working knowledge of vehicle repair basics, need torefresh your memory, or have a specific question, use this book as a just-in-time quick reference.

Need an advanced search? Individual topics and subtopics are listed in theindex by key word.

Special CharactersYoull see some special characters in the margins. Heres what theymean:

Tis symbol indicates a very tasty piece of information that deservesspecial attention.

Well place the NEWsymbol next to any information that repre-sents a recent change in standards or technology. OBD II is a work

in progress: expect the OBD standards and their application to adapt tochanges in vehicle technology.

Gray Boxes!Gray boxes contain OBD II Diagnostic rouble Codes that are commonlyassociated with the condition or fault being described on that page. Tese

are not the only possible codes, but they are likely suspects!

These DTCs are commonly associated with secondary AIR failures:

P0410-P0419 -

Miscellaneous AIR failures

How This Book Is Set Up


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Ignition timing: Incorrect ignition timing has a big effect on emissions.Ignition timing changes as timing be lts or chains stretch. Incorrect basetiming often results from failure to obser ve recommended timing adjust-ment procedures.

Oxygen sensor replacement: Oxygen sensors degrade over time, losingtheir ability to respond quickly to changes in exhaust oxygen. Heatedsensors tend to last longer, but any sensor with over 60,000 miles of useshould be tested with a lab scope to confirm proper switch rates, based onmanufacturer's recommendations.

rottle body cleaninghelps improve idle quality and control. Trottleplates, throttle bodies, and intake manifolds all benefit from periodiccleaning. Removing carbon deposits prevents throttle plate sticking andjust-off-idle vehicle hesitation.

Carbon cleaning/injector cleaning:Both fuel injectors and intake mani-fold air passages should be cleaned at regular intervals. Cleaners reduceintake valve deposits that lead to cold stalling and tip-in hesitation.

Preventing Emissions Problems

Before we start telling you how to diagnose and repair emissions problems,let's look at list of things to check and common maintenance proceduresthat prevent emissions problemsin the first place!

EGR passage cleaning: Particularly recommended where the EGR doesnot flow into the intake manifold plenum, but rather into its own distri-bution system within the manifold. Many deposits can be removed usingapproved chemical cleaners, although heavy deposits may need to beremoved by rodding or scraping.

PCV valves: Use only high quality PCV valve replacements. Increasedemissions, oil leaks, and oil consumption problems can all start withclogged PCV breather hoses and/or valve cover breather or baffle restric-tions. Clean the valve cover and passages and blow the hoses clean withcompressed air.

Oil, air, and fuel filter changes:Prevent problems and excessive enginewear: change fluids and filters at recommended intervals, based on vehicleuse and operating environment. Gasoline dilution of crankcase oil maycause a rich condition as fuel vapors are reintroduced into the intakemanifold through the PCV system. Use the recommended viscosity oil a tall times.

Valve lash adjustmentshave a major impact on emissions and perfor-mance.

Spark plugs, distributor caps and rotors, plug wires:Worn out sparkplugs or secondary ignition components with high resistance or leakinginsulation lie at the root of many emissions problems. Maintain the igni-

tion system for reliability, economy and low emissions.

Preventing Emissions Problems


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The Auto Emissions Bible10

Combustion

Balancing Act

Oxygen and Fuel

Ignition

Engine Basics

Intake Stroke - Suck

Compression Stroke - Squeeze

Power Stroke - Bang

Exhaust Stroke - Blow

Fast Oxidation

Stoichiometry

Combustion By-products - Carbon Dioxide

Combustion By-products - Carbon Monoxide

Combustion By-products - Oxygen

Combustion By-products - NOx

Combustion By-products - HC

Review

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

1Here's a list of common tests you need to know and use if you intendto repair emissions problems successfully.

How many are in your diagnostic tool box and used on a regular basis?

Fuel pump pressure test Fuel pump volume test Fuel pump voltage supply test Engine vacuum test Cranking compression test Running compression test Cylinder balance test Cylinder leak-down test Injector balance/ injector volume test Ignition timing adjustment Ignition firing voltage, including snap throttle KV demand test Ignition coil available KV test Ignition system spark KV leakage test Circuit voltage drop test Exhaust backpressure test Alternator AC voltage ripple test Alternator charging voltage and current test Battery state of charge and load test Lab scope tests: injector voltage and current waveforms Fuel pump current (amp ramp) test Ignition coil current ramping test Scan tool tests, including bi-directional (functional) testing

Catalytic converter oxygen storage capacity test Catalytic converter cranking hydrocarbon efficiency test

Diagnostic Toolbox


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Combustion TriangleModern combustion control technologies improve combustion efficienciesto improve power and fuel economy, and reduce harmful emissions.

o understand how this works, we must first look at the combustion tri-angle.

Fuel- Te fuel used in most spark ignition engines is gasoline.

Oxygen - o burn one gallon of gasoline, youll need about 9,000 gallonsof air. (Now you know why air filters get dirty so quickly!)

Heat- Te heat required to start the combustion process comes from aspark plug that ignites an atomized, pressurized mixture of air and fuel.Te ignition system must be capable of producing and delivering reliablesparks of 30, 40, or even 100 KV thats 100,000 volts!

Well be looking at the engine in more detail as we proceed, but right nowlet's focus on air and fuel.

Combustion

Combustion is a balancing act. Our combustion

triangle shows the three physical components of

combustion: fuel, oxygen, and heat.

Fuel and oxygen combine chemically in the pres-

ence of heat to produce the energy that powers

our vehicles.

Too much or too little of any component results

in incomplete combustion, loss of power, and

increased harmful emissions that pollute our air.

Combustion

heat

fuel

oxygen

comined

under

pressure

OxygenTe oxygen needed for combustioncomes from the atmosphere thatsurrounds us. An internal combus-

tion engine is an air pump. A largevolume of air must be drawn intothe engine to provide the oxygenfor combustion.

Most of the air, about 78% ofit, consists of nitrogen, whosechemical symbol is N, or some-times, N

2.

About 20 to 21% of the atmo-sphere isoxygen. Te chemical symbol for oxygen is O, or O

2. (Te

subscript 2 indicates that it takes two atoms of oxygen or of nitrogen tomake a single molecule of either.)

Te remaining tiny fraction of atmospheric gases is a mixture of many ele-ments and chemical compounds.

FuelFuel is a complicated chemical "soup" made of thousands of chemicalcompounds known as hydrocarbons. Each has its own specific chemicalformula. o keep things simple, we'll refer to them in a group that we'lllabel HC.

In simplest terms, HC is fuel.

For the geeks among

us, most of these fuel

molecules take the form

ofH

nC

m, where n and m

are integers.

Gas


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Both diesel and spark ignitionengines need compression to run.

It's just that the diesel needs

about twice as much compression

to squeeze the air and fuel to the

point of ignition.

Combustion - Ignition

Suck-Squeeze-Bang-BlowTe internal combustion engine is still king of the hill. Internal combustionhas converted fossil fuels into power for our cars and trucks for more than acentury. Early engines used carburetors and magnetos or breaker point igni-

tions to fuel and fire combustion. In a modern vehicle, the Powertrain Con-trol Module (PCM) directs solenoid-operated fuel injectors and electronicignition systems to keep fuel and fire synchronized with engine mechanicalmovements. Te entire process is as finely tuned as the performance of asymphony orchestra.

Internal combustion hinges on mechanical parts of the engine workingtogether as a large air pump.

Pistons move down inside cylinder-shaped bores, sucking in atmosphericair.

Atomized fuel is added to the air. Tis volatile mixture is squeezedandignited BANG.Te resulting explosion strikes the head of a piston,forcing it toward the crankshaft. A rod connecting piston and crankshaftrotates the shaft, and it turns.

At the end of each combustion cycle, the trash needs to be thrown out!Burned out gases are blownfrom the cylinder to the exhaust system, so theprocess can repeat itself.

Let's look at the fourcombustion strokes in moredetail.

Combustion - Engine Cycles

Light My FireTe third and final ingredient of our ignition triangle is heat. In spark-ignition gasoline engines, air and fuel are compressed inside the enginescylinders and then ignited by a spark from an ignition system. Te ignition

system commonly includes a step-up transformer known as an ignition coilthat is connected to a spark plug a t each cylinder.

Tere are two critical parts to spark ignition:

Spark energy (the amount of electrical energy available for the spark)

Spark timing (when the spark occurs during the combustion cycle)

Diesels are compression-ignition engines and have no external ignitionsystem. Instead, they compress the air/fuel mixture inside each cylinder wellbeyond the compression ratios of spark ignition gasoline engines. Increasingcylinder pressure increases cylinder heat until the mixture gets hot enoughto burn.

Compression

While not an ingredient, compression is a conditionrequired for combus-tion. Low compression resulting from an engine mechanical failure reducescombustion efficiency, and may prevent combustion a ltogether.


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intake valve open - exhaust valve closedTe first step in combustion is to fill a cylinder with anexplosivechargeof airand atomizedfuel. (If you've ever blown up a tin can with acherry bomb, you understand the effects of an explosion in a closed con-

tainer.)

A cylinder is filled with air when its piston moves toward the crankshaft(downward in most engines), creating a low pressure inside its cylindricalbore. As the piston moves, the cylinder's intake valve opens, allowing atmo-spheric pressure to push air into the cylinder.

Te computer brieflyoperates a fuel injec-tor to spray atomizedfuel into the incomingair. Te injector staysopen for a very shorttime, so short in fact,that its open time, orON-time, is measuredin milliseconds(thou-sandths of a second).

So far, so good. Wenow have a combus-tible volume of air andatomized fuel inside

the cylinder.

Combustion (Intake Stroke) Combustion (Compression Stroke)

Compression Stroke - SqueezeNow its time to put the squeeze on the gassy mixture in the cylinder. Teintake valve that opened to let the air and fuel enter the cylinder during theintake stroke now closes. With both the intake and exhaust valves closed,

the cylinder is sealed.

Te piston reaches the bottom of the cylinder bore and reverses direction.As it moves upward, it begins to squeeze the air and fuel trapped inside thecylinder. Compression creates heat. Te greater the compression, the hotterthe gases get.

In diesel engines with ex-tremely high compression,the mixture actually getshot enough to self-ignite.

In spark ignition engines,the big bang of the powerstroke is started by a smallbolt of lightning across aspark plug gap inside thecylinder.

Air

Air


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intake and exhaust valves closedAt the right instant, an arc of electrical energy jumps across the spark pluggap, igniting the compressed mixture. Te force of the resulting explosioninside the cylinder depends on several factors, among them the ratio of

oxygen to fuel, the degree of compression, the quality and octane of the fuel,and the timing of the spark event that starts the mixture burning.

When ignited, the gas charge expands rapidly as it burns, exerting greatforce against the only thing in the cylinder that can movethe head of thepistondriving it forcefully toward the crankshaft. It is similar to the forceapplied to a bicycle pedal by your foot: a linear force on the pedal rotates thechain sprocket.

Several unwanted things canhappen inside the cylinder thatresult in incomplete combustion,also known as a misfire. Commonmisfire causes include a weakspark, incorrect spark timing,improper air/fuel ratio, poor fuelquality, and low compression.

Combustion (Power Stroke) Combustion (Exhaust Stroke)

intake valve closed - exhaust valve openAs the piston moves downward, the explosion burns out and its force weak-ens. Burned remains of the combustible charge are similar to the soot andash left over after a wood fire goes out.

Any left over pressure and waste gas material must be exhausted from thecylinder before a new charge of fresh air and fuel enters on the next intakestroke.

During the exhaust stroke, the exhaust valve opens and the next upwardmotion of the piston blows the waste gas out of the cylinder to the exhaustsystem.

Tis completes one entirefour stroke combustioncycle. Te process contin-ues to repeat itself as longas the elements needed forcombustion continue toshow up in the cylinders inthe right proportions at theright times. exhaust

gas


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A Chemical ReactionSo what exactly is this thing that we commonly refer to as combustion? Itsa chemical reaction that causes fuel and oxygen to combine to release energy

by a process known as oxidation.

Rapid oxidation creates the rapid expansionof burning fuel and oxygen that powers ourvehicles. Burning gases push against pistons asa bicyclist pushes on pedals. Te cyclist rotatesa chain sprocket; pistons rotate a crankshaft.Te cyclist and gas engine both oxidize fuel todo this work.

Lets think of an internal combustion engine asa device that creates conditions needed for the

fast oxidation of hydrocarbons.

Heres the simplified general chemical equation for combustion:

O2 + HC + heat --> H2O+ CO2 + more heat

Clean combustion produces energy, harmless water (H2O), and CarbonDioxide (CO2), the same gas we humans exhale.

Dirty combustion is incom-plete burning that produces severalunwanted gases, some of which aretoxic and environmentally hazard-ous.

Along with water and all the

gases mentioned so far, other

combustion by-products in-

clude ammonia (NH3), sulfur

dioxide (SO2), sulfuric acid

(H2SO4), and aldehydes, ke-

tones, carboxylic acids, soot

and polycyclic hydrocarbons.

Combustion (Oxidation Chemistry) Combustion (Stoichiometry)

A Balanced MixtureChemical reactions like oxidation can take place successfully under goodconditions or fail when conditions are bad.

For every chemicalreaction, there is aGOOD mixture ofingredients that willmake the reactionsuccessful if condi-tions are r ight. Tisideal mixture isreferred to as stoi-chiometry.

Stoichiometric con-ditions are differentfor different chemi-cal reactions. Teone we need to lookat here is the one forair and gasoline inan internal combus-tion engine.

Te stoichiometric air/fuel ratio for a compressed mixture of air and gasolineis about 14.7 to 1, by weight. Tat is 14.7 par ts of air to one part fuel, byweight.

Why does it say by weight?

It takes 14.7 pounds of air to burn one pound of fuel, or 14.7 tons of air to

burn one ton of fuel.

A gallon of air weighs far less than a gallon of fuel, so it takes about 9000

gallons of air to combust one gallon of fuel.Unwanted gases targeted for reduction by emissions controls include

HC (unburned fuel), CO (partially burned fuel), and NOx (nitrogen and

oxygen that combine at high combustion temperatures).

12 14 16 18 20 22

12 14 16 18 20 22

Rich

VeryRich12:1

VeryLean22:1

14.7:1 (lambda 1.0)

Lean

targeted gases


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Combustion (by-products) Combustion (by-products)

Carbon DioxideOne exhaust gas is CarbonDioxide (CO2): Carbondioxide is an indicator of

combustion and cata-lytic converter effi-ciency.

CO2 exhaust concentra-tion increases with increasedcombustion and catalystefficiency.

A good running enginewith a properly functioningcatalytic converter produces CO2 concentrations of 15% or more.

CO2 is the result of the complete oxidation of carbon.

Low CO2 readings may indicate a mechanical fault. Tese commonly in-clude problems like low compression, leaking valves or improper camshaftor ignition timing.

Rule of thumb: If CO2 + CO percentages total less than 14.5% (with AIRinjection disabled), check the engines mechanical condition first!

Is that a tailpipe or a downspout?

If you burn a gallon of gasoline, youll generate nearly a

gallon of water. You may have seen the water dripping out

of a cold tailpipe in the morning. When the water is hot

enough, you can no longer see it, but water vapor is still

a major component of exhaust gas emissions. Another

name for water is hydrogen dioxide: its what you get when

you burn the hydrogen (H) component of fuel (HC).

Carbon MonoxideCarbon Monoxide (CO) isa toxic exhaust gas.

Carbon monoxide formswhen hydrocarbons areincompletely combinedwith oxygen. In the exhauststream, CO is an indicatorof an air/fuel ratio imbal-ance occurring when thereis more fuel than can beburned (oxidized) by theamount of oxygen available.

CO is a good indicator of a rich mixture (one containing too much fuelfor the amount of oxygen available).

CO concentrations of more than 1-2% measured upstream of the catalyticconverter indicate a rich running condition.

exhaust

gas

CO: Odorless and Deadly

Breathing CO in concentrations as low as300 ppm (0.03%) can be fatal in 30 minutes

or less.

CO is odorless (exhaust odor is from hydro-

carbons). CO is also a central nervous system

depressant that makes us slow and.

Every garage should have a functioning CO

detector with a digital readout in use at all

times.

OBD DTCs

OBD DTCs

P0420-P0422

P0430-P0432

Low Catalyst Efficiency DTCs

may accompany low CO2.

These DTCs are commonly associated

with high CO:

P0172; P0175

Fuel System Rich

P0190; P0193Fuel Pressure Fault

P0115, P0118P0125- P0128ECT signal high or coolant tem-

perature low; excessive time to enter

closed loop

exhaust

gas


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exhaust

gas

Combustion (by-products) Combustion (by-products)

OxygenOxygen (O2): Tere are several reasons for high concentrations of oxygen inthe exhaust stream:

A lean mixture (one thathas too little fuel for theamount of air).

Operation of an air-pumpor other secondary airinjection system. (Be sure totemporarily disable any sec-ondary air injection system,and ensure that the exhaustsystem is leak-free beforesampling the exhaust.

Exhaust system leakage.

High O2 readings may also result from: an unmetered air leak downstreamof air flow sensor; low fuel pump output; dirty/clogged injectors or a re-stricted fuel filter or fuel supply hose; high electrical resistance in the injec-tor power circuit; a contaminated air flow sensor; cylinder misfire; etc.

DTCs commonly associated with high O2:

P0171; P0174Fuel System Lean

P0300 or P03xxEngine random or cylinder-specific misfire

P0410-P0419Secondary AIR faults

NOxOxides of Nitrogen(NOx):NOx (pronounced knocks)forms when the combustion

chamber temperature exceeds2500F, the ignition point forcompressed nitrogen. Whilehigh NOx readings rarely ac-company a rich mixture, NOxshould be considered as anindicator of high combustionchamber temperatures thatcommonly accompany highengine loads.

NOx has a slight odor and is reddish-brown in very high concentrations. Itcauses a stinging or burning sensation in the nose, eyes, and throat.

High NOx readings may indicate: insufficient EGR flow; overly advancedignition timing; excessive compression (from previous engine work or frominternal carbon buildup due to a previous rich-running condition); cooling

system faults; overly lean air/fuel mixtures; an inoperativeknock sensor; low octane fuel;insufficient fuel pressure orvolume; etc.

OBD DTCs

NOx failures often occur after vehicle

repairs to correct an emissionsfailure from a rich condition (high

HC and CO). Rich running causes

carbon build up inside the combus-

tion chambers. This decreases

combustion chamber size, increasing

compression and heat, the major

causes of NOx.

DTCs commonly associated with high NOx:

P0127IAT High

P0234-P0249Turbo/ Supercharger Faults

P0324-P0334Knock Sensor Fault

P0400-P0409EGR Faults

P0480-485Cooling Fan Faults

OBD DTCs

OBD DTCs

exhaust

gas


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Combustion (by-products)

exhaust

gas

Hydrocarbons

Hydrocarbons (HC): Remember that wereusing HC to represent the many types of

hydrocarbons found in raw gasoline.

HC in the exhaust stream is unburned fuel.It is present in the exhaust whenever it isnot oxidized in the combustion process orby catalyst action.

HC concentrations are usually measuredand reported in parts-per-million (ppm).A good running engine with a properly

functioning catalytic converter should emit fewer than 50 ppm of HC fromthe tailpipe. Many of the best running engines will exhaust fewer than 10ppm HC.

High HC concentrations are of ten associated with poor fuel economy.

Common causes for high exhaust HC:

EVAP system vapor leaks to the intakemanifold

A very rich or very lean mixture Ignition misfire or poor fuel atomiza-

tion. Check ignition first, includingtiming and spark plug heat range.

A leaking EGR valve

Improper cam or ignition timing Worn plugs, wires, or other secondaryignition components

Uneven fuel injector delivery or drip-ping injectors

An external fuel leak will cause high HC

readings in the area of the leak. Make sure

there's no raw fuel dripping near your emis-

sions analyzer test probe.

Tis handy chart summarizes much of what weve learned so far.

Review

Gas Engine Condition

CO2 measure of combustion efficiency

CO rich mixture, too much fuel, not enough air

O2 lean mixture, too much air, not enough fuel

NOx high combustion temperatures, high engine load

HC unburned fuel, leaking fuel or vapors

These DTCs are commonly associated

with high HC:

P0171; P0174Fuel System Lean

P0172; P0175Fuel System Rich

P0300; P03xxRandom or cylinder-specific misfire

P0350-P0362Ignition Coil/Circuit Faults

P0400-P0409Incorrect EGR position or flow

OBD DTCs

Combustion (by-products)


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DTCs

Diagnostic trouble Codes

2Sign PostsWhen the MIL comes on, OBD II doesnt just leave you stranded; it putsup sign posts that point you in the right diagnostic direction.

Tose sign posts are called Diagnostic rouble Codes (DCs) and there arethousands of them. How many exactly? I have no idea, and there is no sensecounting them; more have been added since I wrote this, and there are moreon the way. New components and new technologies demand new labels.

Expect the DC list to grow like weeds in a pea patch. Hybrid-electric

vehicles, gas direct injection, and hi-tech diesel exhaust systems have eachadded entire series of numbers to the master DC list. ighter emissionsstandards and new stricter fuel efficiency standards are generating newtechnologies, daily.

And Now...A Brief Message from the ComputerTe Malfunction Indicator Light (MIL) in your car is illuminated. (Tis isthe warning lamp also referred to as the Check Engine Light).

Our first diagnostic step is to check the vehicle computer for codes. Te

easiest way to look for codes is with a scan tool, although some cars displaycodes on the dashboard odometer or driver information center. Sometimes,well find one DC; sometimes well find several.

When we pull codes from the vehicle computer (PCM), we ask the scantool to send a text message saying, Yo, computer: send me a list of DCs,willya? Te computer responds by firing off the data, which is then dis-played on the scan tool.

Diagnostic rouble Codes are the first computer troubleshooting tool welearn to use, and the one we are genera lly most comfortable with. Knowinghow to use DCs properly is another matter entirely.


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DTCs DTCs

DTC NumbersEach OBD II DCnumber is a five-charac-ter label, made up of both

numbers and letters ofthe alphabet. As a result,DCs are said to bealphanumeric.

A Sample DTCHeres a common DC:P0300

Descriptor = randomengine misfire

P0300 is so common that

professional repair techni-cians know it by heart. Itindicates that there is amisfire in one or more ofthe engine cyl inders. Teexact location of the mis-firing cylinder or cylindersis not given.

Clearly, the DC is point-ing us in the right generaldirection, but its up to us to locate the exact location and cause of the

failure.

Note: Some vehicle computers identify a misfiring cyl inder by number. Infact, newer vehicles are required to do so. For example, P0302 indicatesthat a misfire is occurring in cylinder number 2.

Sign PostsRemember: DCs are sign posts pointing us in a general diagnostic direc-tion.

Google That DTC

Google P0300 and youll get a long list of links

to various web sites, some that that list genericDTCs, and others that cater to those looking for

just-in-time repair information.

The more common the DTC, the more hits youll

get.

In fact, you can G oogle almost any DTC and get

some feedback that may even include a detailed

explanation of the affected circuits, and trouble-

shooting advice.

Some links take you to forums where par ticipants

discuss personal repair experiences. Like all inter-

net information, youll need to exercise caution

when selecting advice.

Some bloggers are reliable; others less so. A few

will recommend procedures that are ineffective,

stupid, or downright dangerous. Play it safe:

cross reference all internet information, and

compare procedures in blog posts to published

repair standards from reputable sources.

The first digitis a letter of the

alphabet that indicates the main

subsystem where the fault occurred.

P = Powertrain

B = Body

C = Chassis

U = Network Communications

The second digit indicates whether

the DTC is defined by the Society of

Engineers (SAE) or by an OEM.

A second P-code digit of 0, 2, or 3 (3400-

3999) indicates an SAE- defined DTC

A second P-code digit of 1 or 3 (3000-

3399) indicates an OEM-defined DTC.

DTC NumberingTe graphic on this page shows how DC numbers are assigned.

Relax, you dont need to memorize this information. In actual practice, youll

pull vehicle DCs from the vehicle, write them down, and look them up ina DC reference book or repair database.

The numbering system below applies specifi-

cally to PowertrainDTCs (those beginning with

the letter P).

For Body (B), Chassis (C), and Network Com-

munications (U) codes, a code with a second

digit of 2 is reserved for OEM DTCs.

The P3xxx code numbers are split; those from

P3000-P3399 are OEM reseved; those from

P3400 to P3999 are SAE reserved.

The fourth and fifth digits are a fault

number assigned to the component

and fault recorded:

Common examples of fault types

include:

circuit fault

circuit low

circuit high

circuit range/performance

The thirddigit indicates the affected

subsystem.

P0Axx - Hybrid

P00xx - P01xx - P02xx - Fuel an Air Metering

P03xx - Ignition and Misfire

P04xx - P05xx - Vehicle Speed, Idle Control,

and Auxiliary Inputs

P06xx - Computer and Auxiliary Inputs

P07xx, P08xx, P09xx - Transmission


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DTCs DTCs

Where Do DTC Numbers Come From?

wo sources:

e Society of Automotive Engineers (SAE).SAE-defined DCs aresometimes calledgenericcodes, since they apply to systems and componentscommonly used in a broad range of vehicles.

Vehicle makers.OEM-defined DCs generally apply to components andsystems that are unique to specific makes or models.

This is a page from SAE paper J2012. This page shows DTC num-

bers listed by SAE, followed by their descriptors. All SAE papers

can be purchased from the SAE book store at www.sae.org.

Whats In a DTC?If you look at a master list of DCs (photo), youll notice that many com-mon components have several DC numbers assigned to them. Each num-ber is labeled to identify the component and type of failure.

DTCs for a Common SensorA good example of a common component is the Engine Cool ant Tempera-ture Sensor (ECT),found in virtually all modern vehicles. A thermistorinside the EC sensor changes resistance in response to changes in enginecoolant temperature. Tis changes EC circuit voltage. Te EC is es-sential for many vehicle computer functions. In fact, the PCM uses ECfeedback when adjusting fuel delivery and ignition timing, controlling theelectrical cooling fans, and detecting engine overheating, just to name a few.

Te DCs listed below tell us that the EC and its circuit can fail in several

ways. Each DC number is labeled by failure type. Since the EC is such acommon component, the numbers below are generic, meaning they are as-signed by the Society of Automotive Engineers (SAE). Tese generic DCnumbers can be used by any OEM to identify common EC circuit faults.

P0115- Engine Coolant emperature Circuit MalfunctionP0116- Engine Coolant emperature Circuit Range/PerformanceP0117- Engine Coolant emperature Circuit LowP0118- Engine Coolant emperature Circuit - HighP0119- Engine Coolant emperature Circuit - Intermittent

DescriptorsSee how each DC number is identified by a short label? Well call theselabels descriptors. Engine Coolant Circuit Low is a descriptor. It names thecomponent and fault condition.

But it doesnt give exact details, does it?


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Troubleshooting Tip

Many inexperienced mechanics automatically

replace any component mentioned by the DTC

descriptor. Be careful with this approach: looseor corroded connections or damaged wiring

are very often the underlying cause of sensor

problems.

For example, while a P0117might indicate a

bad ECT sensor, the descriptor clearly indicates

a problem in the ECT circuit. The ECT sensor is

certainly part of the ECT circuit, but it is not the

entire circuit.

When diagnosing any circuit, include the sensor

connector, sensor circuit wiring, the PCM, the

sensor ground, etc., as well as the sensor itself.

This applies to all sensors.

What Descriptors Tell UsDC numbers and descriptors carry some information. Tey are sign posts,not exact addresses. Its like the difference between, they went thatawayand, they went 240 Elm Street.

Lets run down the list of generic codes for the EC.

P0115tells us only that an undefined fault has been detected in the ECcircuit.

P0116gets a little more specific, but not much. Apparently, the ECsignal is out of range,or its performance issuspicious.

P0117is also more spe-cific than P0115: the

sensor signal is high.Tis tells us that signalvoltage or frequencyis greater than thetest limit. Tis usuallyindicates that theresa break in the wiringbetween the PCM andsensor thats causing anopen circuit.

P0118shows the other

extreme, a sensor whosevoltage is too low; be-low the test limit. Tisusually indicates thattheres a short circuitto ground betweenthe PCM and sensor.If P0117 is heads,P0118 is tails.

SAE v. OEM DTCsLets idle by the curb for a minute here, and talk more about the differencebetween SAE-defined DCs and OEM-defined DCs.

If you look up a P0117, it will have the same descriptorwhether its usedfor a Hyundai or a Hummer. Te second charactera zerotells us it sgeneric: it applies to a common component found on manycars.

OEM-defined DCs are very different. If Zombie Motors uses a reverse-widget-gravitator not found in any other brand, they will choose an OEM(manufacturer-specific) DC number. Te component is proprietary.

Look It Up to Be Sure

OEM-assigned DC numbers have very different DC descriptors, some-times even when they share the same DC number. An illustration worksbest here: we grabbed a random OEM-DC and started looking up the

number for different vehicles. Clearly, a P1107, manufacturer-specific DCmeans different things to different OEMs.

P1107 - Subaru- AIR System Diagnosis Solenoid Circuit FailedP1107 - Honda/Acura- Barometric Pressure Sensor Circuit Low VoltageP1107 - General Motors- MAP sensor Intermittent Low VoltageP1107 - Isuzu- MAP sensor Intermittent Low VoltageP1107 - Audi- O2 Sensor Heating Circuit, Bank2-Sensor1 Short to B+P1107 - Ford- Dual Alternator Lower Circuit Malfunction (Powerstrokediesel)P1107 - Ford- Manifold Absolute Pressure (MAP) sensor circuit intermit-tent low voltage

Here we see that a single DC numberP1107has been used by mul-tiple OEMs to designate very different faults.

It pays to look up DTC numbers and

their exact denitions.


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Yo, Listen Up!Tis next part is very important, because you cannot make repairsunless you know the exact nature of the fault and the test standardsthat will be used to decide if your repairs are effective.

DTC Descriptor v. DTC DefinitionHow does a vehicle manufacturer choose one DC number out of thou-sands to describe a fault? We cant be sure, can we? Tat stuff all happensbehind the curtain back in Oz.

An OEM could conceivably slap a P0115 (Engine Coolant emperatureCircuit Malfunction) on allEC circuit problems. (Heck, malfunctioncould mean anything.) Tis is frowned on.

Ideally, for low circuit voltage, theyll go with a P0117. Do we know morewith the P0117 than we did with the P0115? Some. But I am hungry formore information that will help me fix the car.

I want the exacttest limits. I want steak and potatoes test values that Ican measure! Does a sensor fail at 3.5 volts or at 5.0 volts? Give me teststandards with hair on their chests, expressed in volts or frequency; unitsof pressure or degrees of temperaturethings I can measure with normalshop equipment.

I want to know the exactvehicle operating conditions required to run anonboard test. Is afrumple sensortested as soon as the ignition is switchedon? wo minutes after the engine is started? When driving at 35 mph, orfaster? I want to knowthese things so I can test under similar operatingconditions.

I want to know if there are special operating conditions needed to run anonboard test. Will the test be suspended (delayed) during some drivingconditions?

I want more information than the code number and descriptorgive me. Iwant a definition, chock full of test data. Vehicle repair is a science experi-ment that demands accuracy; it aint horse shoes! If somebody sends medriving directions that say: I live East of Chicago, I wont leave the houseuntil I call back and get an exact street address. Descriptorsare sign posts;Definitionsshould provide the house number!

SAE paper J2012 - Diagnostic Trouble

Code Definitions, establishes the num-

bering conventions for OBD II DTCs.

Oops, theres that word definitions

again. Not the best choice. While J2012

certainly contains a list of generic DTCs

with descriptors, it certainly has no

codedefinitions.

Thats because DTCs get their defini-

DTC Definitions

Heres what a well-written DC definition does for us:

It lists the conditions needed to run a test.Is it enough to have the keyon for a test to run? Does the engine have to be running? Do we need tobe traveling down the road at a minimum speed?

It spells out the test limits.est limits are the answer key for eachonboard test. All pass-fail test limits should be expressed as a calculatedvalue (e.g. degrees of temperature) or as voltage.

Experience with real world OEM repair information tells us thatsome DC definitions are better written than others. Good onesare rich with test data; others are thin on the details, and say aslittle as possible.

Where Do DTC Definitions Come From?Each time an OEM assigns a DC number, it defines the DC.

In fact, once a DC is as-signed to a vehicle, it is nolonger generic. Even an

SAE DC has a vehicle-specific definition once it isassigned to a specific vehicle.

Its descriptor is generic; itsdefinition is specific to thevehicle.

Tats why we have beeninsisting that there is a dif-ference between descriptorand defintiion.

DTCs


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DTCs DTCs

Examples

A well-written DC definition is a great place to look for monitor testconditions and pass-fail standards.

Te following examples are a partial list from GM for an SAE-definedP0117. All are from the same model year, but notice that the DC defini-tion changes as P0117 is applied to different models.

Tese definitions all start from the same DC number (P0117) and sharethe same descriptor (ECT sensor Circuit Lo w Voltage); but the detailsspelled out in the definition tell us they are notall the same.

After the engine has run f or at least 128 seconds, the PCM detectsan EC input of more than 289 degrees F.

Engine run time over 15 seconds, the PCM detects an EC input

of over 284 degrees F; the condition lasts for at least 15 seconds.

Code conditions: is code may be set only if there are no othercodes already stored in memory.Te PCM will store a P0117 if itdetects an EC sensor input greater than or equal to 304 degreesF, either condition met for 2 seconds.

Engine runningthe PCM detects an EC voltage input of lessthan 0.78V for 5 seconds.

Remember:Tese definitions are all used with P0117 in different modelsfrom the same OEMin a single model year! Tree test limits are given in

degrees of temperature; while one lists a test voltage standard. Some requirea minimum engine run time; others do not. One size does not fit all.

If we want to know which measurement standards to use during testing, weneed to look up the DC definition or locate the test standards in a repairdatabase.

Pending DTCs

Sometimes, the PCM stores a DC right away, in a single trip. Sometimes,it needs to see the fault happen again on a second trip before it will store a

full-blown DC and turn on the MIL.

One Trip DTCA first trip DC is stored by a One-Trip Fault. Expect this to be used withclear-cut faults like shorted and open circuits in critical engine sensors.

Two-Trip DTCFaults that must be detected a second time to illuminate the MIL are calledwo-trip faults. Makes sense. wo trip fault detection is used to keep pre-vent falsely illuminating the MIL.

Pending DTCsIn theory, a wo-rip DC should store a Pending DC, the first time thefault is detected. Pending codes do not turn on the MIL, but they shouldshow up on the scan tool. Te Pending DC should be a troubleshootingtool; it should give you fair warning that trouble may be brewing. It is alsohelpful when you want to verify the success of a repair in a single trip.

Te bad news: in real life, there are many vehicles that clam up when askedto display Pending DCs. Te newer the vehicle, the more likely it is thatyoull see DCs on the scan tool.


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Freeze FrameFor many years before OBD II came along, skilled professional techniciansused their scan tool to make data recordings. Tey would start the record-ing manually when they experienced a symptom, or set up the scan tool to

trigger on a DC or an event of their choosing. Tese multiple frame datarecordings were called movies. Another tool was a single frame capture asnapshot to store data from a one moment in time.

Logically, OBD II is set up to store its own data snapshot. Te data camerais triggered when a DC is stored, grabbing a snaphot of emissions data.Tis single frame of event data is called a Freeze Frame.

Te OBD II standard requires that at least oneFreeze Frame be stored, usu-ally with the first DC. Tere is an exception: if a more serious DC occursafter the first, the original Freeze Frame may be overwritten by data fromthe newer and more serious DC.

All Freeze Frame data is stored with the DC until both are erased fromthe vehicle computer.

Te amount of data youll get from a Freeze Frame varies. Te original datalist is pretty short, although newer models provide more data.

Well talk more about Freeze Frame later, in the troubleshooting section.

Putting DTCs to WorkA DC is a tool. Like any other tool, its usefulness depends on the skill ofthe user. Keep the following in mind whenever you use DCs:

e PCM occasionally points the finger of guilt at an innocent victim!A transmission DC may be stored if the ransmission Control Module(CM) fails to see a critical sensor signal input like the vehicle speed orthrottle position sensor.

Some vehicle problems will not store a DTC, even if the problem isemissions related.For example, a component that is binding or stickingmechanicallybut passes the electrical testmay not store a code.

A vehicle with DTCs stored in memory may have no symptoms; this ismore common than you think.

Example:A dead or gutted catalytic converter will store a DC: the

catalyst isnt cleaning the exhaust, but the car will run perfectly.

Example:An evaporative emission system vapor leak (maybe from aloose gas cap?) may illuminate the MIL, but have no effect at all onvehicle performance.

Sophisticated PCM fail-safe strategies keep many vehicles movingdown the road, even when something is broken. Te PCM just takesover and plugs in a sensor value to keep the engine running. Forexample, the PCM may substitute the air intake sensor signal if itcannot see the signal from the engine coolant sensor.

Some symptoms wont not store DTCs.Te flip side of the previous coinis that OBD II will occasionally run some active tests that cause brief

symptoms. Tese may seem like a problem, but are not. For example,an onboard self-test strategy may produce a brief rolling idle while fuelvapors are purged from the charcoal canister into a running engine. Tis isnormal in some vehicles. Dont rush to fix something that is not broken!

DTCs may not tell us the entire story.An open circuit in a shared electri-cal circuit may affect several sensors, even though only one fault is identi-fied by the DC. Problems in shared voltage supply and ground circuitscan affect many components at the same time. Makes it tougher to findthe reason.


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DTC Cautions and Pitfalls

Some DTCs identify asystemproblem not an faulty individual com-ponent.Youll have a deuce of a time d iagnosing a low purge flow DC

until you have some knowledge of how the purge system works. o correcta low purge flow condition, you first need to know what purge flow means.Ten you need to know which components control purge flow. When theyoperate. Where they are located.

A vehicle with multiple faults may not store multiple codes.OBD IIis designed to reduce the old problem of cascading faults. Tis was a lotbigger problem in previous onboard test systems when a single fault startedan avalanche of codes. o prevent cascading DCs, one or more OBD IImonitors may stop running altogether when a DC is stored. With somemonitors asleep, additional faults are not detected. o get the monitorsrunning again, correct the original fault, and erase DCs. Well cover thisin more detail in the chapter on Monitors.

A vehicle with multiple DTCs may have a problem unrelated to any ofthe codes found in memory.For example, a voltage drop in a commonsensor ground connection can disrupt multiple circuits. Tis drives thePCM bananas, and it misdiagnoses the problem, spewing a list of non-sence in the process.

One Fault = Multiple Codes

A single fault in an electrical circuit can drive several components batty at the same time.

Example: 2003 Chevrolet Suburban 1500 5.3L

Symptom:When driving over bumps, the Anti-lock Brake System (ABS) light and Red brake light

come on. The MIL may flicker ; power door locks lock and unlock; the chime sounds.

The following DTCs are stored:

C0237 stored in the ABS system.

P0706 stored in the Powertrain Control Module (PCM).

B1000 stored in the Transfer Case Control Module (TCCM).

U1000 stored in the Instrument Panel Cluster (IPC).

Confirmed Fix:Tighten or repair loose or damaged ground wires at the rear of each cylinder head

(grounds G103 and G104).

(Our thanks to the good folks at ww w.Identifix.comfor this case study from their hotline archive.)

DTC Cautions and PitfallsDTCs in the hands of the novice can result in serious injury (or worse).Tis is particularly true of hybrid vehicles where lethalvoltages may be en-countered. Hybrid vehicle faults involving high voltage DCs should always

be referred to a properly trained professional with access to the recommend-ed safety and test equipment, and vehicle-specific documentation.

This Hybrid Electric Vehicle battery packs 275 attention-getting, heart-stopping volts

enough to seriously injure or kill an ususpecting human who sticks his finger in the wrong

place. We stronglyurge do-it-yourselfers to leave diagnosis and repair of high voltage

hybrid vehicle systems to properly trained and equipped professional technicians.

DTC symptoms may be difficult to predict in complex systems. Tis isespecially true where network communication codes are involved. Manymodern cars are have several computers connected over a network. Networkproblems store DCs that start with the letter U.

U-code faults can be hard to find. Te skill level required to isolate a U-codefault depends on:

the number of networks installed in the vehicle; how the networks are connected; whether the fault still present; whether the failure occurs with the engine off or with the engine running.

Like hybrid vehicle faults, network troubleshooting commonly requiresspecial test equipment, exact vehicle repair data, a lot of patience, or all ofthe above.


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Keep Things SimplePlay the odds. It is far better to seek simple solutions to common problemsthan to waste hours looking for unlikely solutions. Te KISS rule: Keep ItSimple, Stupid, is always a high probablity choice. Most of the time, a DC

will point you in the general direction.of your problem.

Lets say you pull a P0118 (engine coolant temp input high). Freeze Framedata for the DC records a -40 EC temperature. Odds are, youll find abad EC or a wiring fault. (If you hear hoof beats, think horses, not zebras!)

Exceptions to the RuleIts also good to remember that stuff happens. Sometimes the OBD makes amistake and blames the wrong suspect.

Sam Bell ace mechanic and owner of Te Lusty Wrench in ClevelandHeights, Ohio shared thos real world experience with us:

A Toyota with a P0125(insufficient coolant temperature for closed loopfuel control) sure sounds like a vehicle that isnt reaching normal operatingtemperature, doesnt it? Probably a bad thermostat, right? No necessarily. Ev-ery time this fault has shown up at our shop, the real cause has been a faultyO2 sensor (or a faulty air/fuel sensor, in vehicles that have them).

Volvo P0118:this is the same EC input high DC used as an exampleabove, but this time with a twist. Look carefully at Freeze-Frame. If theEC is anything but -40, this one does have a bad -stat! Its hangingopen, keeping the engine too cool for too long, so the EC input is higherthan expected, hence the code choice.

Fords with a P0401(insufficient EGR flow): needs a new DPFE sensornine times out of, well, nine!

Exceptions to the Rule

A GM 3.1L minivan with a P0171(Fuel System Lean, Bank 1) maybe running lean, but based on lies told to us before by these vehicles, our

money rides on a sluggish oxygen sensor.

o check the O2 sensor response, add propane at the air cleaner hous-ing inlet, and see if the O2 voltage rises. If the voltage doesnt increase,stick a fork in the O2 sensor and replace it: its cooked. (Of course ifyou have access to an exhaust gas analyzer, check the overall air/fuelratio to see whether the PCMs fuel trim corrections are keeping thingsrunning in stoichiometry. Tats just a fancy way of saying an air/fuelratio that is being controlled in its normal target range.

How about a Toyota with two DTCs: P0441 and a P0446? (EvaporativeEmission System Incorrect Purge Flow) and (Evaporative Emission SystemCanister Vent Solenoid Fault), respectively. Odds are high that the problem

lies in the EVAP Bypass VSV (Vacuum Switching Valve), which the PCMuses to switch the Fuel ank Pressure Sensor from reading tank pressure toreading canister pressure.

Not to pick on Toyota, but another misleading code o ccurs in some Toy-otas with a P0401 (Insufficient EGR Flow).est for EGR control vacuumduring a road test. Ten listen for a noticeable rough running conditionwhile manually opening the EGR at 1800 rpm. If both these tests pass,replace the EGR VSV or solenoid. Te real problem isnt insufficient EGRflow, its that the flow doesnt start soon enough.


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Shotgunning, Trouble Trees, andProfessional Grade Diagnostics

Each section of this book is designed to prepare you for real world trouble-

shooting. Tere are several ways to attack vehicle repairs, including:

Shotgunning -Tis approach is simple: replace parts until the car is fixed.Inefficient and costly, this is the least desirable repair method.

Trouble Trees -rouble trees provide a guided diagnostic path to walk usthrough a repair process, step by step. Made of simple tests and if-thenchoices, the tree is commonlly drawn on a paper as a series of text-filledboxes filled with directions, choices, and test values. o use the trouble tree,start at the top, follow the directions in the boxes, and arrive at a conclu-sion at the bottom of the tree. a Da!Te final boxthe repair recommendationusually sounds something

like: Replace with known good widget and retest. rouble trees have reallimitations.

Professional Grade Diagnostics- Skilled, experienced repair technicianscommonly dislike trouble trees for the same reason Lance Armstrongwould hate the thought of having training wheels installed on his bike. oomany limitations! Skilled techs get there faster by using the DC definedtest standards.

If the DC definition is poorly written and light on facts, a smart tech willpan through the trouble tree too, looking for test values; extracting diagnos-tic nuggets.

Armed with this wealth of information, the tech attacks the problemscientifically, using traditional pinpoint tests performed withwith a digitalmultimeter, a fuel or vacuum gauge, a scan tool, etc.

Tis diagnostic approach improves the speed, accuracy, and verification ofthe repair. Its the professional grade approach.

We recommend it.

Get More from DTCs:

Look up the code definition. Dont limit yourself to the descriptor.

Compare test standards in the DC definition to actual vehicle condi-tions.

Compare data values to test standards. Do test values match up todatastream and freeze frame?

Use any test conditions listed in the definition to simulate the conditionspresent when the DC was stored.

We hope youve gained a little respect for DCs after all this. Originallydesigned as an easily accessible diagnostic tool, the DC shouldnt besomething you rush past on your way to a more complicated solution.

Professional application of defined test standards, under similar test condi-tions, is a fast and effective way to locate and repair many failures that storeDCs.


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Permanent DTCs

o prevent cheating on scan tool emissions tests, a new type of DC hasbeen proposed, called a Permanent DTC. Unlike previous DCs that can

be erased with a scan tool (or by removing battery voltage from the PCM),the Permanent DC is stored in an area of PCM memory that is not erasedwhen power is removed.

Any MIL-illuminating DC will be a Permanent DC. Expect this changeto be phased in between 2010 and 2012. Permanent DCs will be identifiedby a unique label to identify them from previous DCs.

Tis is an important change from previous DC erasure. In the past, it hasbeen possible to pass a test with a DC in memory if the MIL test passesand enough monitors have run to completion.

The MIL 3Babel-iciousTere was a serious effort made by OBDs founding fathers to standardizecommon terms and component names; that way, everybody would speak thesame language.

Te second thing you learn about OBD II is that a lot of people didnt getthat memo. Standardizing anything in the automotive field is like simplify-ing the Federal tax code. Better to spend your time learning to fly by flap-ping your armsitll happen sooner and takes far less energy.

For instance: SAE paper J1930 suggests that we call the OBD warninglight the Malfunction Indicator Lamp, or MIL. In response to this plea forstandardization, some passive aggressive folks like GM used the old illumi-nated Check Engine Light(CEL) le tters, instead. (Perhaps GM wasnt thebest example of strategic planning.)

And the Winner for Best Term Is...Malfunction Indicator Lampis the better term; its more inc lusive. Weprefer it. Check Engine Light is a weak choice by comparison, since OBDmonitors not only the engine, but the transmission, fuel vapor recoverysystem, and any other component or system that might cause an increase inharmful emissions.

Te short form of Malfunction Indicator LampMIL is pronouncedmill by some, or by saying the names of its individual lettersemm-eye-ell. Since SAE didnt explain how to pronounce it (like it would havehelped), pay your money and take your choice.

Your are officially warned: from here on out, we will refer to the MalfunctionIndicator Lamp as the MIL.


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MILMIL

Got Some Black Tape?OBD II did some teething when it was introduced, and gained a reputa-tion in some circles for being a little cranky at times. Other words used todescribe it during its awkward infancy inc luded: moody, balky, worthless,

less-than-worthless, and several other shop terms too vibrant for this politecompany.

As OEM engineers worked furiously to iron out its wrinkles, many motor-ists routinely ignored the MIL; others covered it with black tape if it cameon. (Its lying anyway, right?) More ambitious technophiles pulled the bulbor cut the wire. Crude, Dude, but effective.

And so it was, that early on, MIL illumination was often viewed as a falsealarm. Te two major reasons:

OBD II software in some makes was as trustworthy and predictable asWindows Vista. Early systems got a waiver, the equivalent of a Mul-

ligan on the golf course or a Get Out of Jail Free card in Monopoly. Ifpart of the diagnostic system had more bugs than an old barn, it got anexemption. Honda just disabled the misfire monitor in some makes, andfound it easier to pay the fine and compensate vehicle owners.

Tere was no penalty for ignoring the MIL. (Te first reason was amplejustification for the second reason in many motorists minds.) Tats whythe MIL became known to many motorists as that stupid light, orstoooopid light if you are from the Big Apple.

OBD II Coming of Age - State Emissions Tests

Gradually, OBD II sofware improved. In fact, its reliability was deemed sogood that state emissions tests started to use a MIL test and scan of vehicle

emissions data as a replacement for tailpipe testing.

Te advantages of Scan Tool Emission tests were too great to ignore:

Te test equipment for a scan test is WAY cheaper than the cost ofitanic-sized, 10-ton emissions analyzers needed for tailipe testing.

Scan ool tests are faster, cleaner, and less dangerous than running acouple tons of vehicle on a dynamometerinside a building.

Its easier to sell the motoring public a fast, quiet, hi-tech scan. People trustcomputers more than they trust other people.

ailpipe test accuracy depends in part on several variables that called theiraccuracy into question in some circles. Vehicle operating temperature andthe skill of the employee behid the wheel during the test could both have abig impact on the final results.

All scanned emissions data can be sucked out of the vehicle computer andpiped to a mainframe miles away over phone lines, untouched by humanhands. Employees at test centers could even use a bar code scanner to entercritical vehicle data, including its Vehicle Identifiction Number (VIN).Tis moves cars through test lanes faster and reduces many errors associ-ated with manual data entry.


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MILMIL

Does the MIL Matter?If you live in an area where emissions tests are done with a Scan ool test,its pretty hard to ignore an illuminated MIL. Remember this vehicleowner: MIL status passes or faisl a vehicle in the first stage of the Scan ool

emissions test.

Tis is no small deal, ladies and gents: if the car fails, you dont get newlicense plates until the vehicle is fixed and passes a retest.

First, the MIL TestWhen you pull into the vehicle emission test center, the first thing theycheck is the MIL.

Te MIL must come on when the ignition is first switched to the onposition. Tis is called a bulb check, and its used to confirm that the bulbis still in the dashnot in your tool box or pocketand that it is beingcommanded by the vehicle computer.

Te MIL must go out and stay outwhen the engine starts.

If the MIL doesnt illuminate key-on and go out when the engine starts,the vehicle fails the testperiod. Tere is no room for interpretation.

KOEO stands for Key-On-Engine Off

You perform these tests every time you start

your car. Just make sure the MIL comes on with

the key in the on position, and that it goes off

when the engine starts.

Tamper-proof?We Americans are a resourceful lot, and many back yard inventors havetried to game the OBD II system over the years. Some folks always feel thatcheating to pass the test is easier than fixing the car.

A few creative characters have tried to fool the Scan Tool test by wiringthe MIL to the oil pressure switch.Tink about it: the oil light comes onkey-on-engine-off, and then goes out when the engine starts. (Tats thecreative spririt that made America great!)

Others have tried to use a good car to get a b roken car through the test.Several test station strategies are now used to prevent this, and newermodels can be identified by scanning their Vehicle Identification Number(VIN). (Its like a pro athlete juicer who sends in a blood sample donatedby his steroid-free brother.) Matching the vehicle registration and VINprovide fingerprint-positive vehicle identification in later model vehiclesto prevent this activity.

The visual MIL check is followed by a scan of the vehicle computer. The

command sent by the computer to the MIL better match its actual state (ON

or OFF). If the MIL command says ON, but the MIL is OFF with the engine

running, the motorist has some explaining to do. Thats why MIL status shows

up in datastream.


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MIL Fun Facts

Te vehicle computer, referred to as the Powertrain Control Module, con-trols the MIL.

Te PCM can turn off the MIL. Te OBD II test that turned on the MILinitially must run and pass three times for the PCM to turn off the MIL.

Te MIL illuminates when the first DC is recorded in the PCM. Ad-ditional DCs do not change MIL il lumination after the first DC isrecorded. Te MIL stays on until it is turned off by the PCM or by a com-mand from the scan tool to erase DCs.

If you disconnect the vehicle battery long enough, all vehicle data stored inthe PCM is erased. Tis turns off the MI, at least temporarily.

Te MIL in OBD II vehicles works differently when compared to onboard

diagnostic systems used before OBD II. In most ear lier self-test systems,an intermittent fault can cause the MIL to go on and off repeatedly duringa single vehicle trip. Once the MIL is on in an OBD II vehicle, however, itstays on for at least three trips, unless you erase DCs manually.

You can turn off the MIL with a scan tool by erasing DCs. Unfortu-nately, this also resets all test results stored in the PCM to their defaultvalue. Te vehicle will not pass a Scan ool emissions test in this condition.It must be driven to complete those tests again before it can be tested. (Seethe chapter on Monitors in this book for a more information.)

The DLC 4Say AHHHHH!Te Data Link Connectoris where you plug in the OBD II scan tool. Wellrefer to simply as the DLC. Te DLC has a standardized shape, with 16cavities.

Some DLC cavities are filled with electrical pins,; others are empty.

Some pin functions are mandatory; others are optional.

Some pins are used for power and ground; others carry data.

Optional pins are used at the d iscretion of the OEM (vehicle maker).

Te standardized DLC shape means you dont need a box of speciallyshaped cable ends for your OBD scan tool interface. One size fits all.

Power to the PeopleAny OBD II-compliantcable end fits any OBD IIDLC. In fact, the stan-dardized DLC connectorhas created a whole newmarket in scan tools. Nowanyone can purchase anaffordable generic scantoolor a laptop computerloaded with scan soft-wareto the DLC.

Pin 1 = DiscretionaryPin 2 = Bus(+)Line J1850Pin 3 = DiscretionaryPin 4 = Chassis GroundPin 5 = Signal GroundPin 6 = CAN HighPin 7 = ISO K Line (9141-2 and 14230-4)Pin 8 = DiscretionaryPin 9 = DiscretionaryPin 10 = Bus(-)Line J1850Pin 11 = DiscretionaryPin 12 = DiscretionaryPin 13 = DiscretionaryPin 14 = CAN LowPin 15 = ISO L Line (9141-2 and 14230-4)Pin 16 = Battery (unswitched minimum 4 amps)

16 15 14 13 1 2 1 1 10 9

8 7 6 5 4 3 2 1


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DLCDLC

Connect the Scan Tool

With the ignition switch turned to the OFF position, plug the scan toolcable connector into the DLC. Align the connector carefully as you push it

in; dont try to force it into the DLC at an angle.

Damaged pins at the scan tool cable end or DLC cause an assortment ofdata transfer problems, and may prevent communication altogether.

Depending on the scan tool configuration, the cable connector may nothave all 16 pins.

Expect pins 4 and 5 (grounds) to extend outward farther than the rest; thisis normal.

Te DLC shape is standard, although some pin assignments vary by make,model, and data protocol.

Depending on the scan tool configuration, the cable

connector may not have all 16 pins. Expect pins 4 and 5

(grounds) to extend outward farther than the rest; this is

normal.

DLC Quick Tips

Te DLC shape is the same on all OBD II-compliant vehicles.

Te DLC has cavities for a maximum 16 electrical connections. Expect tosee several empty cavities in the DLC.

Te DLC should be located in the general area between the driver doorand the right side of the center console. More recent standards narrow thiszone, keeping the DLC on the drivers side of the centerline, higher thanthe base of the steering column.

Te most common DLC location is beneath/behind the lower edge of thedash panel in the area near the steering column.

Some DLCs are hidden in odd places or concealed by trim panels, ashtrays, or carpeting. Some DLCs are actually located at the rear of the cen-

ter console. (Tis is done by an engineer with too much time on his handswho wants to make the DLC more accessible to your rear seat passengers.We all know how much your mother-in-law loves to watch data on herscan tool on a long trip!) Later regs also eliminate this silliness, as well.

DLC damage may prevent data exchange between the scan tool andvehicle computer.

A vehicle with a damaged or missing DLC cannot undergo a computer-ized scan tool emissions test.

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DLC

OBD IIDiagnosticConnector

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87654321Finding the DLC

OBD specifications indicate

the general area for mounting

the DLC. Ideally, youll find it

between the driver side door

and right side of the center

console. Most of the time,

youll find the DLC beneath

the lower edge of the dash-

board, often tucked away, up

behind the lower edge of the

panel for protection.

The DLC shape is the same on all

OBD II-compliant vehicles.


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87654321At rear ofcenter consolein ashtray

Behindtrimpanel incenter console

beneathsteeringwheel

insideauxiliaryfuse box

behind trimpanel in dash

behind ash trayinsideauxiliaryfuse box

insideglove box

behind trimpanel in right

side ofcenter console

below dashnext to centerconsole right

beneath trimpanel in centerconsole

Other DLC Hiding Places

While the DLC is easily located and readily accessible beneath the dash inmost cars, there are enough exceptions to annoy. Some OEMs have taken a

perverse pleasure in showing how cute they can be when it comes to hidingthe DLC.

A few foreign cars (what-ever that means!) are repeatoffenders: VW and BMWbuilt in a default layerof frustration with theirpatented snap-and-breakplastic dashboard cover pan-els; Honda/Acura has beenknown to use what I callthe Easter Egg approach,

hiding the DLC behind theashtray or mounting it onthe right side of the centerconsole behind a carpet flap.(CAUION: Some of thedashboard trim/cover panelsare very expensive.) When in doubt, consult a repair database, shop manual,or other information source to locate a hidden DLC.

DLC DamageIn areas where vehicle emissions are tested with a scan tool, the DLC mustbe accessible and undamaged, or the vehicle fails the test. If DLC damageprevents scan tool communication, the DLC must be repaired, and commu-nications restored to allow testing.

When all else fails... read the directions! If the DLC isnt visible, take agood look at the underside of the steering column. Tis is where the vehiclemanufacturer is supposed to put a sticker telling you just where the DLC ishidden. Be sure to check with your chiropractor before attempting this, orany other, under-dash gymnastics routine!

Sneakier hiding places for the DLC include: behind ashtrays; beneath a carpet flap on the

right side of the center console; and beneath fragile dashboard trim pieces. You may even

find the DLC at the very rear of the center console, mounted there for ease of access by rear

seat passengers who may want to plug in their scan tool for entertainment.

The OBD Clearinghouse has a downloadable pdf listing DLC locations.

http://www.obdclearinghouse.com/files/dlc-database.pd

This one mounts sideways.

Is this upside down, or right side up?

It all depends on the vehicle and whether

or not you are standing on your head at

the moment.

10 of the 16 cavities in this DLC contain elec-

trical connections; the others are open.

Use extreme caution when removing dashboard trim covers; some will not tolerate ham-

fisted removal techniques. These delicate plastic covers are painfully pricey.

DLC DLC


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Connection CautionsIve been working on cars too long to take anythingfor granted. Sometimesthe simplest mistake sets us up for failure, embarrassmentor both.

So be careful and please observe these DLC cautions:

Check your scan tool cable end for signs of wear or damage, especiallybent pins. Do so each time you connect to a DLC. rying to cram a bentcable end connector pin into the DLC is a bad way to start a diagnosis.

Plug the cable end squarely into the DLC; dont try to force it in at anangle. Tis is not always as easy as it sounds, especially if the DLC ismounted at an awkward angle in an inaccessible location.

CAUTION: Avoid kicking the connection.Some DLC locations andextra long scan tool cable ends leave the cable hanging awkwardly beneaththe dash, where it is easily kicked. Easy does it: a swift kick from a 12D

work shoe can render the serial interface senseless. (Been there; done that.)

One mans beef:

Now that most DLCs are being located in a semistandard loca-

tion beneath the driver side dash, I want to know why. If you

are a working technician, or anybody who might want to drive

a vehicle with the scan tool attached, why would you want the

scan tool cable handging down from the dash, right where you

can kick it?

Why not place the DLC higher in the dash, somewhere away

from my size twelves? I am a repair technician, not a place-

kicker.

DLCDLC

Some vehicle computers get stupid if the scan

tool is connected with the igntion switch in

the ONposition: a few will even erase data or

recalibrate. For safety sake, we recommend that

you turn the ignition switch to the off position

before connecting or disconnecting a scan tool.

Heres an example:

Tech Service Bulletin: All 2003 - 2004 Mazda 6

and 2005 Mazda6 2.3L only.

Description:

Some customer vehicles may have a false MIL

illumination with multiple U-code DTCs. This

condition may be caused if the WDS DLC cableis connected or disconnected while the ignition

switch is in the ON position, or when the engine

is idling.

Important: When connecting or disconnecting

any scan tool equipment to the DLC-2 connec-

tor (under dash), the ignition switch must be in

the OFFposition; otherwise, the MIL may come

ON and false CAN communication DTC codes

may be set in the different CAN bus modules.

The following DTCs may be stored if this condi-

tion occurs:

U1900-ABS; U2516-ABS; U1900-FF-IC; U2516-

FF-IC; U0073-FF-PCM; U0073-FF-TCM; U0100-

FF-TCM

It has been reported that some customer

vehicles have failed the state emission OBD II

test. This may be caused by the inspection sta-

tion connecting or disconnecting the DLC cable

when the ignition switch in the ON position, or

when the engine is idling.

Careful there, Sparky.

Leave the ignitionswitch OFF until

the scan tool cable isplugged securely intothe DLC: then turn theignition switch to theON position, or startthe engine.

ruth be told, thou-sands of scan tools areconnected and discon-nected every day whilethe ignition is turned onor the engine is running,

with no ill effects. Butthere are some vehiclesthat break out in a rashwhen this is done, and Idont want nasty letterssaying I didnt warn youof the possibility.

Te sidebar on this pageillustrates one exampleof the kinds of problemthat can be caused byleaving the ignition inthe ON position whileplugging in or discon-necting your scan tool.

Other makes have beenknown to get PCMamnesia or erase theodometer reading.


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DLCDLC

10001001

01100100

11011000

PCM Read DTCsErase DTCs

View Datastream

View Monitors

View Freeze Frame

The PCM and scan tool exchange voltage pulses that are interpreted into meaningful data.

The scan tool is the interface between machine and man, converting raw numbers into

words and measured values we can understand.

Texting the Vehicleexting is all the rage with young cell phone users, but OBD II computershave been doing it for years! Its hard to think of a car computer as hip ortrendy, but OBD II may have been ahead of its time!

Te scan tool and PCM exchange information like two-thumb typists ex-change text messages. Te process is similar. After you plug in the scan tool,the next step is to turn the ignition to the ON position or start the engine.At this signal, an OBD II scan tool and PCM exchange greetings, agree touse the correct data language, and establish a communication link.

An OBD II-compliant scan tool should check the data link and select thecorrect data protocol (language), automatically. Well talk more about dataprotocols next, just remember that even the so-called generic interface mayuse one of several languages to communicate. (So much for standardization.)

A Necessary EvilJust when were picking up speed, we need to tap the brakes here and men-tion data protocols, an important issue for two major reasons:

Te scan tool must text messages to the PCM using the correct data pro-tocol. Each protocol is a unique computer language. An OBD II-compliantscan tool should recognize the correct protocol and select it, automatically.(If I speak Spanish and you speak English, our conversation wont get far,will it?)

Each data protocols has a maximum transmission speed, by design. Wellsee why this is important, shortly.

First generation OBD II vehicles useone of three generic data transmissionstandards (some folks split the J1850standard into two protocols, for a total

of four). Why all these options wereused or allowed is a mystery to me tothis day. It added a need less layer ofcomplexity, and none of the protocols isfast enough to get a speeding ticket in aschool zone.

Original OBD II Data Protocols ISO 9141-2- Tis protocol limpsalong at a very slow 10.4 kbps. Commonin early Chryslers and many imports. SAE J1850- Tis protocol includestwo subprotocols that operate at differ-ent pulse widths and transmit at differ-ent speeds: SAE J1850 Pulse Width Modulated (PWM) used by Ford (41.6kbps), and SAE J1850 Variable Pulse Width (VPW) used by several OEMs(10.4 kbps). ISO 14230-4 - (10.4 kbps) Keyword Protocol 2000, used by EuropeanOEMs. Similar to ISO 9141-2 but with enhanced diagnostic messages.

Note:Tis is not something youll need to memorize. If your scan tool isworking properly, it should automatically detect and use the vehicle proto-col.

Warning: Some early OBD II data

interfacesstill cause cuss and

mumble moments by refusing to

talk to the first scan tool plugged

into the DLC. The cure is often assimple as switching to a scan tool

from another tool company. Many

professional repair shops keep

multiple scan tools handy for this

reason. to keep data flowing in the

largest number of vehicles. Thank-

fully, most generic communications

problems have been resolved; just

keep them in mind when working

on last century OBD II vehicles.


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DLC Review

Communication occurs over a serial interface where data is sent be a seriesof voltage pulses.

Te scan tool should automatically detect the correct data protocol andselect it to allow communications.

If your scan tool will not communicate with a vehicle, it pays to try a dif-ferent scan tool before resorting to more complcated diagnostics.

Some early interfaces had programming issues that prevented certain scantool and PCM match-ups.

Generic scan interfaces before CAN are slow. Controller Area Network(CAN) interfaces are much faster than the original OBD II protocols.

DLC

Datastream 5Spies Everywhere!Datastreamis exactly what its name suggests; its a stream of data carriedover a wire by voltage pulses. Pulse sequence, amplitude, and duration can bearranged into patterns that carry information. An analogy to Morse Codeshould work here, assuming you didnt sleep through American History inmiddle school.

Using a scan tool plugged into the standard OBD II data port, a carbonbased life form can text the vehicle computer and ask for information. If allgoes according to plan, the PCM gets the message and texts back the desired

data. (Heck, youve seen Scott do this on Star Trekto make sure the warpengines are working.)

Small Things Make Me HappyIf you ask it to do so, the PCM will stream data that contains info about theexact status of various vehicle operating parameters, related to vehicle emis-sions.

Tis may seem like a ho-hum event until you realize that OBD II brokesome major ground by allowing this text exchange to happen as it does. In1996, when there was absolutely nothingstandard about scan tool interfaces,this was a bigfriggin deal. I was still working on many cars then that had noserial data capacity at all!

Ten came OBD II. All at oncefor the first time everanyonecouldconnect a standardscan tool to a standardizeddata connector, and look ata standardset of data parameters. Te generic data list for emissions wasadmittedly a short one, but a welcome improvement, nonetheless.


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Datastream DatastreamWhats a PID?A simple picture of a datstream display should get us off on the right track.Heres a list of generic vehicle data parameters.

Right now, these dont mean a lot to you, but they wil l. Each item in this listis a parameter, and each parameter stands for a component or system that

reports to the vehicle computer.

Parameters have labels and a shorthand reference. For example, the EngineCoolant Temperaturesensor is identi-fied by name and also by its three-letterabbreviation: ECT.

Parameters and their IDentification labelsare commonly referred to as PIDs. Youllbe seeing this term a lot from here on out.

Each PID has its own value, sent by asensor or by a claculation inside the PCM.

Tese values are listed in a column to theright. Some values are listed in commonmeasurement scales like percent, degrees oftemperature, units of pressure, or volts.

Eventually, youll need to know what thesevalues mean, and whether they representnormal or abnormal operation.

In a repair shop, youll hear

technicians refer to the ECT

PID or the O2 sensor PID

when they discuss a line-item

in datastream.

If one of the values listed next

to a PID looks funky, you may

hear a technician say some-

thing like, That O2 sensor PID

is not changing. Or, That O2

sensor PID is too low.

Now that youve got the lingo,

lets move on.

Data Display SamplesHere are sample datastream displays on d ifferent scan tool screens. Each ofthese is a dedicated scan tool and its screen is pretty small compared to PCbased scan tools with large monitors.

This scan tool from Actron lists all PIDs, with

room for 8 separate items per screen. The

arrows to the right of the screen indicate that

additional PIDs are available by scrolling.

This inexpensive scan tool from AutoLink

costs well under a hundred bucks. It displaysa maximum of four PIDs per screen, so

expect to scroll to view all PIDs.

Even this professional grade scan tool

displays only nine PIDs per screen.


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Datastream Datastream

Original OBD II Generic DatastreamTe MIL is on. You have retrieved DCs. Now its time to look at genericdatastream to see if the conditions that stored the DC are still present.

OBD II generic datatream displays a select number of emissions-relateddata parameters that have a direct and significant effect on engine perfor-mance, fuel control, and emissions.

Generic PID LisLook at the items in thegeneric PID list on thispage. Tese PIDs maybe viewed live in genericdatastream using a genericscan tool.

Te i

Documents

New Emissions Book 7-28