permission granted to reproduce for educational use only. 2 © goodheart-willcox co., inc. chapter...

© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.2

Chapter 13

Troubleshooting Techniques


Objectives

Explain the basic principles of driveability diagnosis.

Evaluate driver input concerning vehicle problems.

Make visual checks for underhood problems.

Perform a road test.

Describe the basic methods of diagnosing driveability problems caused by engine systems.


Objectives

Explain the basic methods of diagnosing driveability problems caused by the vehicle drive train.

Describe the basic methods of diagnosing driveability problems caused by computer control systems.

List factors to be considered when deciding to adjust, rebuild, or replace parts.


Troubleshooting

Ability to accurately troubleshoot separates successful automotive technicians from “parts swappers”

Ability to apply logical diagnostic process can be improved with study and experience


Evaluating Customer Input

Obtaining information from driver is first and most important part of diagnosis

Often allows some preliminary testing to be bypassed

Allows technician to focus on most likely source of problem


Driver Input

Try to talk to person who normally drives vehicle

Try to get accurate description of problem before beginning any work

Driver can usually provide some idea of past service problems and maintenance

Carefully evaluate what driver says


Driveability Worksheet


Assessing Driver Input

Try to estimate driver’s attitude and level of automotive knowledge

Driver can unintentionally mislead technician

Pay attention to:Hand gestures

Body language

Simulation of noises heard



Most customers are not familiar with automobile operation

Never accept driver’s diagnosis until you verify it

Driver may be overreacting to normal condition



Owner may downplay symptoms, hoping for inexpensive repair

Never give uninformed estimates, even if problem seems obvious

Explain to customer diagnostic charge is more cost effective than paying for service that may not fix problem


Difficult People

Reasons for anger or hostility varyProblem was not solved during previous visit

Customer fears repairs will be too expensive

Customer is upset over inconvenience

Customer is in bad mood unrelated to vehicle problem


Difficult People

Dealing with customers requires tact and understanding

Talk in calm tones

Avoid getting angry yourself

Keep owner informed about repair process as frequently as possible


Difficult People

Allow customers to feel they are part of diagnostic and repair process

Once problem is located, inform customer of cause and what is needed to correct problem

If practical, show customer defective part and explain why it is defective


Work Order

Legal contract with vehicle owner

Fill out completely, even for simple services

Begin work order by listing date and filling out:

Customer information

Vehicle information, including VIN


Work Order

After work is finished, list:All work performed

Labor time

Labor cost

Parts needed and cost of parts

Total of any subcontracted work

Supply charge

Disposal fees


VIN Numbers


Emission-Certification Label

Located in engine compartment

Contains information on:Recommended spark plug gap

Ignition timing

Routing diagram for hoses


Road Testing

Road test may:Reveal or confirm driveability problems

Indicate specific problem areas and what further tests need to be made

Determine that perceived driveability condition is normal, and no further testing is needed


Road Testing

Some problems can only be found by road testing

Most problems reveal themselves in less than 15 minutes

When possible, try to duplicate exact conditions under which driver says problem occurs


Road Testing

Always try to road test with ownerEnsures owner and technician are talking about same problem

Saves valuable time

Avoids diagnosis and repair of problem that does not fix what customer wanted fixed


Road Test Safety Considerations

Before beginning road test, check to ensure vehicle can be safely driven

Check:Exterior damage

Tire inflation and condition

Turn signals, brake lights, horn

Brake pedal

Steering wheel



Address any safety-related equipment problems before road testing

Check vehicle fuel level

Wear seat belt at all times

If radio is on, turn it off



Drive slowly when leaving service areaEnsure brakes and steering are working properly

Ensure no other problems exist that could cause personal injury or vehicle damage



Obey all traffic rules

Be alert while drivingIf necessary to monitor scan tool readings or look for problem while vehicle is driven, have assistant drive as you monitor the situation


Road Testing Procedures

Try to duplicate normal driving conditionsLight and heavy acceleration

Deceleration

Braking

Different cruising speeds



Note response of engine and related systems

Be alert for:Noises or vibrations

Harshness

Engine miss or hesitation

Transmission shifts

Operation of brake and steering systems



When specific problem is identified, look for conditions related to problem

Note if other vehicle parts or driving conditions affect problem

Note all factors related to problem before returning to shop


Diagnosing Intermittent Problems

Very difficult to diagnose

Usually occur only under certain conditions

Can be related to:Temperature

Humidity

Certain vehicle operations

In response to certain tests by ECM


Diagnosing Intermittent Problems

Try to recreate exact conditions under which problem occurred

If road testing does not duplicate problem, other types of testing will need to be done

Essential to closely follow principles of strategy-based diagnostics


Performing Visual Inspections

Check for visible problems before performing diagnostic tests

Use sight, smell, hearing

If problem is not related to cold operation, leave engine running at first

Stop engine before investigating any part near hot or moving parts



(Ford)



While under hood, check level and condition of:

Engine oil

Coolant in recovery tank

Automatic transmission fluid

Note any leaks

Note any disconnected hoses or air intake ducts



Check air and PCV filters for clogging

Make sure PCV valve and hose are not plugged

Check condition of drive belts, especially alternator belt

If engine has serpentine belt, check condition of belt tensioner



Look for prior work on vehicle if no history available

Signs of abuse or tampering

Any engine part that has been removed or replaced by non-stock parts

Aftermarket add-on equipment that can affect vehicle operation


Principles of Diagnosis

Be sure you correctly interpret all information

Correct root cause of failure

Check simple things first

Make educated guess rather than uneducated guess

Remain calm


Using Service Information

Service information is source of all:Vehicle specifications

Diagnostic procedures

Expected test results

Repair procedures

First determine which type of information is needed


Using Service Information

Service information is available as:Manufacturer and general information

Troubleshooting charts

Electrical, vacuum, and information flow schematics

Be sure to use specific information for model and year of vehicle

Protect service information from damage


Troubleshooting Charts


Schematics

Traces path from beginning of wire, hose, or information trail to its end

May show how information flows to and from ECM

Make copies of needed pages and trace on copies, not original


Diagnosing Electrical Problems

Minor electrical defects can become major problems

Having accurate wiring schematics is crucial

First, photocopy schematic for system to be diagnosed


Diagnosing Electrical Problems

Begin at power source and physically trace wiring back to system ground connection

As each connector, length of wire, and component is tested and checked, mark off component on photocopy

You will eventually isolate the defective wire, connector, or component


Diagnosing Charging and Starting Systems

Observe operation as engine runs

Charging systemCheck voltage and amperage output

Check for voltage spikes

Starting systemObserve cranking speed and perform cranking amperage test


Diagnosing Charging and Starting Systems

If starting problem is caused by parasitic draw, begin checks at fuse block

Pull fuses one at a time until circuit causing draw is isolated

Copy schematics for affected circuits and trace each circuit until problem is isolated


Diagnosing Engine Problems

Check fuel, ignition, and compression systems first

Unless there is good reason to look at another part of vehicle

More than one part of single system may cause same symptom



Check all possible causes of problem in basic engine systems before making repairs

Dynamic compression test is common diagnostic method

Cylinders are disabled individually



After fuel, ignition, and compression systems are tested, check:

Emissions system

Cooling system

Lubrication system

Exhaust system



Make visual inspection for disconnected hoses or wires

If visual inspection does not reveal problem, check operation of entire system



You may need to check cooling system for internal leaks or check engine oil pressure by installing pressure gauge

If suspected system is controlled by ECM, check for related trouble codes



Sometimes, problem can only be determined by partial disassembly

Before considering major engine disassembly, all other possibilities should be reconsidered and eliminated


Diagnosing Computer Control Systems

Before beginning diagnosis on vehicles equipped with on-board computers:

Obtain proper service information and other information for computer system

Thoroughly check all non-computer systems

Check ECM memory for trouble codes



ECM monitors out-of-range readings from:

Sensors

Output devices

ECM itself

Readings are stored as trouble code



If MIL is on or flashing, ECM contains trouble codes

If MIL is not on, ECM may still contain stored codes

Always perform code retrieval process before proceeding further

Once codes are identified, make further tests as identified in service information



Process of elimination isolates computer system parts that cannot be tested

ECM

Ignition module

Start by testing all parts that can be tested

If all testable parts check out okay, non-testable part is most likely cause


Procedures for Computer System Diagnostics

Driveability problems may be caused by defects not related to ECM or ECM-controlled system

Always look for obvious problems first

If no obvious defects are found, retrieve trouble codes from ECM memory



Find out what code indicates, and look for defects that could set that code

If basic engine and drive train systems are operating correctly, computer control system may be at fault



Check all electrical connectors for tightness and cleanliness

Check input sensors and related wiring first

Most common cause of problems



Next, check:Output solenoids and other output devices

Motors

Ignition modules

Injectors

If input devices, output devices, and related wiring are okay, ECM is defective


KOEO and KOER Test Procedures

Tests performed with ignition on and either engine running or not running

Key-on, engine-off (KOEO) tests

Key-on, engine-running (KOER) tests

Comparing KOEO and KOER readings often helps to pinpoint problem


Diagnosing Drive Train Problems

Drive train parts can affect driveability by incorrectly transmitting engine power

Defective pressure switches can send improper signals to ECM

Defective solenoids can fail to perform ECM output commands

Other problems include noise, vibration, and harshness from worn parts


Diagnosing Drive Train Problems

Some defects can be spotted by raising vehicle on lift, such as:

Worn U-joints or CV joints

Oil on clutch facings

Other problems will only show up when vehicle is driven


Manual Clutch and Transmission/ Transaxle Diagnosis

Manual clutch problems can cause slipping, vibration, and chatter

Check clutch by slowly engaging it with:

Engine running

Vehicle stopped

Transmission in first gear

(Subaru)


Automatic Transmissions and Transaxles

After checking level and condition of transmission fluid, drive vehicle enough to shift through all speed ranges

Check that shifts are smooth, without slippage, and occur at proper times and speeds


Automatic Transmissions and Transaxles

If used, try adjusting throttle linkage, then recheck shift pattern

Check that torque converter clutch is applying when it should

If problem cannot be corrected by adjustments, refer to service information for repair procedure


Diagnosing Other Vehicle Systems

Systems affecting driveability include:Brakes

Front and rear suspensions

Steering system

Air conditioner

Cruise control



Check and inspect each system’s components

Look for obvious problems, including missing or loose drive belts

Look for loose electrical connections on alternator and air conditioning



Check air conditioning for:Proper refrigerant charge

Problems that could make compressor cycle excessively or affect engine operation

Refrigerant leaks at fittings



When possible, drive vehicle to detect problems

Road test may quickly located problems in suspension, brakes, and cruise control system

If symptoms or codes occur in road test, but not in shop, defect may be in system operating when vehicle moves


Diagnosing Problems Caused by Aftermarket Equipment

Add-on equipment may cause problems due to:

Improper installation

Electromagnetic interference

Poor connections to battery power and chassis ground are most frequent mistakes


Diagnosing Problems Caused by Aftermarket Equipment

Examine system for proper installationTight connections

Components installed in locations that do not interfere with other systems

Wiring cleanly routed, tied together, and preferably installed in plastic looms


Diagnosing Problems Caused by Fuel

Gasoline-related driveability problems should be considered if vehicle has problems such as:

Hard starting

Hesitation

Surging

Rough idles before engine reaches normal operating temperature


Diagnosing Problems Caused by Fuel

If vehicles systems appear okay, suggest owner try another gasoline brand

If owner uses premium in vehicle that does not require it, suggest lower grade

Using wrong grade of diesel fuel in diesel engine may cause driveability problems in cold weather


Deciding on Needed Work

Process of interpreting results of all diagnostic tests

Before condemning part based on test results, review its interaction with engine and vehicle systems

Decide if part in question can cause particular test reading or symptom


Deciding on Needed Work

Troubleshooting charts and other diagnostic data can be great asset

Good troubleshooting chart:Lists all possible causes of problem

Allows parts to be checked in logical sequence


Always Perform Additional Tests

Additional testing is especially important when suspected part is solid-state, or otherwise untestable device

Most are too expensive to randomly replace

Making further checks to confirm problem is always good idea


Deciding on Proper Repair Steps

Amount and type of needed corrective actions must be determined

Parts that interact with defective part may also need to be changed

For example, replacing rotor when distributor cap is replaced


Deciding on Proper Repair Steps

Some parts, while theoretically serviceable, are almost always replaced

Factors to consider when deciding to adjust, rebuilt, or replace part:

Ease of adjustment

Need for special tools

Cost of replacement part

Possibility that old part will fail again


Making Adjustments

If part is easily adjustable, adjust it before rebuilding or replacing

Do not get too involved in trying to adjust stubborn problem

If there is any doubt about whether adjustment has corrected problem, replace part


Special Tools

Used to adjust or disassemble complex assembly

May be good investment if tools can be reused


Rebuild or Replace?

Weigh investment in materials and time against cost of new part

Price of new or remanufactured part is often less than charge to rebuild old part

Many repair shops and vehicle manufacturers recommend replacement of complete assemblies


Contacting Owner about Needed Work

After determining parts and labor necessary to correct problem, contact customer for authorization to perform repairs

Never assume customer will want work done



Defective part or problem may be covered by warranty or guarantee

Vehicle must be returned to approved service facility for repairs

If vehicle is leased, leaseholder is actual owner and may have to approve repairs



Vehicle may be covered by extended warranty or service contract

Forms of insurance

Necessary to file claims for expenses

In some cases, approval must be granted from insurer before repair work can begin



Before talking to anyone about vehicle, be prepared to supply this information:

Exactly what needs to be done and why

Careful breakdown of both part and labor costs

Approximate time when vehicle will be ready



If it is suspected that problem will require further disassembly, make sure customer understands:

Further diagnosis may be needed

Costs may increase


Follow-Up after Repairs

Recheck vehicle to ensure problem has been corrected

Check that vehicle operates properly and meets emission standards

Always recheck vehicle, even if defect is minor

Problem may have been easily fixed, but caused by another vehicle defect


Follow-Up after Repairs

After work is completed, inspect vehicle for tools

Finally, check vehicle for oil, grease, and visible fingerprints


Review

What is troubleshooting?

The process of diagnosing the cause of a given problem.


Review

What is a work order?

A legal contract between the repair facility and the customer that describes the work to be done.


Review

When road testing a vehicle, _____.

A. try to duplicate all normal driving conditions

B. drive quickly from the service area to test acceleration

C. ask the customer to wait at the shop

D. None of the above.

A. try to duplicate all normal driving conditions


Review

What is an educated guess?

A reasonable decision based on testing and the process of elimination.


Review

Which three systems should be checked first when diagnosing an engine problem?

The fuel, ignition, and compression systems should be checked first.


Review

True or False? If the MIL is not on, the ECM does not contain trouble codes.

False


Review

Manual clutch problems can cause _____, _____, and _____.

slipping, vibration, chatter


Review

What must be considered when deciding whether to rebuild or replace a part?

The investment in materials and time must be weighed against the cost of a new part.

permission granted to reproduce for educational use only. 2 © goodheart-willcox co., inc. chapter...

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