ASE Mechanics Engine Performance & Diagnostics — Questions and Answers
Question 1: What is the primary purpose of an engine control module (ECM)?
- To control only the air conditioning system
- To regulate fuel injection and ignition timing (Correct answer)
- To monitor tire pressure only
- To adjust the radio settings
Correct answer: To regulate fuel injection and ignition timing
The ECM manages engine functions such as fuel injection, ignition timing, and emissions control to ensure optimal performance.
Question 2: Which sensor is responsible for measuring the oxygen levels in the exhaust system?
- Throttle position sensor (TPS)
- Oxygen sensor (Correct answer)
- Mass airflow sensor (MAF)
- Coolant temperature sensor
Correct answer: Oxygen sensor
The oxygen sensor monitors exhaust gases to help adjust the air-fuel mixture for efficient combustion and lower emissions.
Question 3: What could cause a vehicle to have poor fuel efficiency?
- Overinflated tires
- Faulty oxygen sensor or clogged injectors (Correct answer)
- Properly functioning fuel injectors
- Clean air filter
Correct answer: Faulty oxygen sensor or clogged injectors
Factors such as faulty oxygen sensors, clogged fuel injectors, and incorrect tire pressure can lead to decreased fuel efficiency.
Question 4: Why is it important to diagnose misfires in an engine?
- Because misfires improve fuel efficiency
- To prevent engine damage and performance issues (Correct answer)
- To reduce exhaust noise
- Because they increase engine speed
Correct answer: To prevent engine damage and performance issues
Engine misfires can lead to reduced power, poor fuel economy, increased emissions, and potential damage to engine components if not addressed.
Question 5: What tool is commonly used to diagnose engine problems by retrieving trouble codes?
- Tire pressure gauge
- OBD-II scanner (Correct answer)
- Multimeter
- Compression tester
Correct answer: OBD-II scanner
An OBD-II scanner is used to retrieve diagnostic trouble codes (DTCs) from the engine control module, aiding in pinpointing engine issues.
Question 6: Which of the following is a symptom of a failing catalytic converter?
- Increased fuel efficiency
- Reduced engine performance and rotten egg smell (Correct answer)
- Quieter exhaust noise
- Lower emissions output
Correct answer: Reduced engine performance and rotten egg smell
A failing catalytic converter can cause reduced engine performance, increased emissions, and a rotten egg smell due to unprocessed fuel vapors.
ASE Mechanics Engine Performance & Diagnostics
What is the primary purpose of an engine control module (ECM)?