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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.

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Chapter 13 l.jpg

Chapter 13

Troubleshooting Techniques


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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.


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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.


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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


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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


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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



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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


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Assessing Driver Input

  • Most customers are not familiar with automobile operation

  • Never accept driver’s diagnosis until you verify it

  • Driver may be overreacting to normal condition


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Assessing Driver Input

  • 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


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Difficult People

  • Reasons for anger or hostility vary

    • Problem 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


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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


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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


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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


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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



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Emission-Certification Label

  • Located in engine compartment

  • Contains information on:

    • Recommended spark plug gap

    • Ignition timing

    • Routing diagram for hoses


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Road Testing

  • Road testmay:

    • 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


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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


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Road Testing

  • Always try to road test with owner

    • Ensures 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


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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


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Road Test Safety Considerations

  • 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


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Road Test Safety Considerations

  • Drive slowly when leaving service area

    • Ensure brakes and steering are working properly

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


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Road Test Safety Considerations

  • Obey all traffic rules

  • Be alert while driving

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


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Road Testing Procedures

  • Try to duplicate normal driving conditions

    • Light and heavy acceleration

    • Deceleration

    • Braking

    • Different cruising speeds


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Road Testing Procedures

  • 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


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Road Testing Procedures

  • 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


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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


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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


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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



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Performing Visual Inspections

  • 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


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Performing Visual Inspections

  • 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


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Performing Visual Inspections

  • 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


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Principles of Diagnosis

  • Be sure you correctly interpret all information

  • Correct root cause of failure

  • Check simple things first

  • Make educated guessrather than uneducated guess

  • Remain calm


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Using Service Information

  • Service informationis source of all:

    • Vehicle specifications

    • Diagnostic procedures

    • Expected test results

    • Repair procedures

  • First determine which type of information is needed


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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



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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


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Diagnosing Electrical Problems

  • Minor electrical defects can become major problems

  • Having accurate wiring schematics is crucial

  • First, photocopy schematic for system to be diagnosed


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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


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Diagnosing Charging and Starting Systems

  • Observe operation as engine runs

  • Charging system

    • Check voltage and amperage output

    • Check for voltage spikes

  • Starting system

    • Observe cranking speed and perform cranking amperage test


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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


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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


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Diagnosing Engine Problems

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

  • Dynamic compression test is common diagnostic method

    • Cylinders are disabled individually


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Diagnosing Engine Problems

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

    • Emissions system

    • Cooling system

    • Lubrication system

    • Exhaust system


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Diagnosing Engine Problems

  • Make visual inspection for disconnected hoses or wires

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


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Diagnosing Engine Problems

  • 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


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Diagnosing Engine Problems

  • Sometimes, problem can only be determined by partial disassembly

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


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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


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Diagnosing Computer Control Systems

  • ECM monitors out-of-range readings from:

    • Sensors

    • Output devices

    • ECM itself

  • Readings are stored as trouble code


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Diagnosing Computer Control Systems

  • 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


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Diagnosing Computer Control Systems

  • 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


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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


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Procedures for Computer System Diagnostics

  • 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


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Procedures for Computer System Diagnostics

  • Check all electrical connectors for tightness and cleanliness

  • Check input sensors and related wiring first

    • Most common cause of problems


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Procedures for Computer System Diagnostics

  • 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


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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


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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


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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


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Manual clutch problems can cause slipping, vibration, and chatter

Check clutch by slowly engaging it with:

Engine running

Vehicle stopped

Transmission in first gear

Manual Clutch and Transmission/ Transaxle Diagnosis

(Subaru)


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Automatic Transmissions and Transaxles chatter

  • 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


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Automatic Transmissions and Transaxles chatter

  • 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


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Diagnosing Other Vehicle Systems chatter

  • Systems affecting driveability include:

    • Brakes

    • Front and rear suspensions

    • Steering system

    • Air conditioner

    • Cruise control


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Diagnosing Other Vehicle Systems chatter

  • 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


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Diagnosing Other Vehicle Systems chatter

  • Check air conditioning for:

    • Proper refrigerant charge

    • Problems that could make compressor cycle excessively or affect engine operation

    • Refrigerant leaks at fittings


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Diagnosing Other Vehicle Systems chatter

  • 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


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Diagnosing Problems Caused by Aftermarket Equipment chatter

  • Add-on equipment may cause problems due to:

    • Improper installation

    • Electromagnetic interference

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


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Diagnosing Problems Caused by Aftermarket Equipment chatter

  • Examine system for proper installation

    • Tight connections

    • Components installed in locations that do not interfere with other systems

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


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Diagnosing Problems Caused by Fuel chatter

  • 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


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Diagnosing Problems Caused by Fuel chatter

  • 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


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Deciding on Needed Work chatter

  • 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


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Deciding on Needed Work chatter

  • 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


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Always Perform Additional Tests chatter

  • 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


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Deciding on Proper Repair Steps chatter

  • 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


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Deciding on Proper Repair Steps chatter

  • 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


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Making Adjustments chatter

  • 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


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Used to adjust or disassemble complex assembly chatter

May be good investment if tools can be reused

Special Tools


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Rebuild or Replace? chatter

  • 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


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Contacting Owner about Needed Work chatter

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

  • Never assume customer will want work done


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Contacting Owner about Needed Work chatter

  • 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


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Contacting Owner about Needed Work chatter

  • 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


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Contacting Owner about Needed Work chatter

  • 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


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Contacting Owner about Needed Work chatter

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

    • Further diagnosis may be needed

    • Costs may increase


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Follow-Up after Repairs chatter

  • 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


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After work is completed, inspect vehicle for tools chatter

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

Follow-Up after Repairs


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Review chatter

What is troubleshooting?

The process of diagnosing the cause of a given problem.


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Review chatter

What is a work order?

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


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Review chatter

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


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Review chatter

What is an educated guess?

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


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Review chatter

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

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


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Review chatter

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

False


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Review chatter

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

slipping, vibration, chatter


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Review chatter

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.


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