Certificate Of Qualification Automotive Service
Technician (310S) Practice Exam Questions And
Correct Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant Download Pdf
1. What is the primary purpose of an engine compression test?
A. Measure oil pressure
B. Check valve timing
C. Determine cylinder sealing ability
D. Test fuel injector flow
Answer: C
Compression testing evaluates how well each cylinder seals during
the compression stroke.
2. Low compression in one cylinder is most likely caused by:
A. Faulty alternator
B. Worn piston rings
C. Restricted exhaust
D. Dirty air filter
Answer: B
Worn piston rings allow compression to leak into the crankcase.
3. What tool is commonly used to measure cylinder leakage
percentage?
A. Vacuum gauge
B. Compression gauge
C. Leak-down tester
, D. Manometer
Answer: C
A leak-down tester measures air loss from a pressurized cylinder.
4. Blue exhaust smoke usually indicates:
A. Coolant burning
B. Excess fuel
C. Oil consumption
D. Ignition misfire
Answer: C
Blue smoke is caused by engine oil entering the combustion
chamber.
5. A flashing malfunction indicator lamp (MIL) indicates:
A. Minor fault
B. Maintenance reminder
C. Severe misfire
D. Sensor calibration error
Answer: C
A flashing MIL warns of catalyst-damaging misfires.
6. Which component regulates fuel pressure in a return-type fuel
system?
A. Fuel pump
B. Fuel rail
C. Pressure regulator
D. Injector
Answer: C
The regulator maintains consistent fuel pressure.
, 7. What is the function of an oxygen sensor?
A. Measure intake air temperature
B. Monitor exhaust oxygen content
C. Control ignition timing
D. Regulate fuel pressure
Answer: B
Oxygen sensors provide feedback for air-fuel ratio control.
8. A lean air-fuel mixture can cause:
A. Black smoke
B. Engine knock
C. Reduced emissions
D. High fuel consumption
Answer: B
Lean mixtures raise combustion temperatures and can cause
detonation.
9. Which sensor primarily affects cold engine operation?
A. MAP sensor
B. Oxygen sensor
C. Engine coolant temperature sensor
D. Throttle position sensor
Answer: C
The ECM relies on coolant temperature for cold-start enrichment.
10. The main purpose of the catalytic converter is to:
A. Reduce engine noise
B. Improve fuel economy
C. Reduce harmful emissions
D. Increase exhaust flow
Technician (310S) Practice Exam Questions And
Correct Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant Download Pdf
1. What is the primary purpose of an engine compression test?
A. Measure oil pressure
B. Check valve timing
C. Determine cylinder sealing ability
D. Test fuel injector flow
Answer: C
Compression testing evaluates how well each cylinder seals during
the compression stroke.
2. Low compression in one cylinder is most likely caused by:
A. Faulty alternator
B. Worn piston rings
C. Restricted exhaust
D. Dirty air filter
Answer: B
Worn piston rings allow compression to leak into the crankcase.
3. What tool is commonly used to measure cylinder leakage
percentage?
A. Vacuum gauge
B. Compression gauge
C. Leak-down tester
, D. Manometer
Answer: C
A leak-down tester measures air loss from a pressurized cylinder.
4. Blue exhaust smoke usually indicates:
A. Coolant burning
B. Excess fuel
C. Oil consumption
D. Ignition misfire
Answer: C
Blue smoke is caused by engine oil entering the combustion
chamber.
5. A flashing malfunction indicator lamp (MIL) indicates:
A. Minor fault
B. Maintenance reminder
C. Severe misfire
D. Sensor calibration error
Answer: C
A flashing MIL warns of catalyst-damaging misfires.
6. Which component regulates fuel pressure in a return-type fuel
system?
A. Fuel pump
B. Fuel rail
C. Pressure regulator
D. Injector
Answer: C
The regulator maintains consistent fuel pressure.
, 7. What is the function of an oxygen sensor?
A. Measure intake air temperature
B. Monitor exhaust oxygen content
C. Control ignition timing
D. Regulate fuel pressure
Answer: B
Oxygen sensors provide feedback for air-fuel ratio control.
8. A lean air-fuel mixture can cause:
A. Black smoke
B. Engine knock
C. Reduced emissions
D. High fuel consumption
Answer: B
Lean mixtures raise combustion temperatures and can cause
detonation.
9. Which sensor primarily affects cold engine operation?
A. MAP sensor
B. Oxygen sensor
C. Engine coolant temperature sensor
D. Throttle position sensor
Answer: C
The ECM relies on coolant temperature for cold-start enrichment.
10. The main purpose of the catalytic converter is to:
A. Reduce engine noise
B. Improve fuel economy
C. Reduce harmful emissions
D. Increase exhaust flow
