ASE Advanced Engine Performance Specialist 2 — Questions and Answers
Question 1: A wide-band (air/fuel ratio) oxygen sensor differs from a conventional narrow-band sensor primarily because it can:
- Only switch between rich and lean at stoichiometry
- Measure the exact air/fuel ratio across a wide range (Correct answer)
- Operate without a heater circuit
- Read only in open loop
Correct answer: Measure the exact air/fuel ratio across a wide range
Wide-band sensors use a pump cell to report the precise AFR across a broad range rather than just switching at stoichiometry.
Question 2: A vehicle shows high long-term fuel trim (e.g., +25%) at idle but normal trim at cruise. The MOST likely cause is:
- A worn timing chain
- A vacuum leak (Correct answer)
- A restricted exhaust
- A faulty knock sensor
Correct answer: A vacuum leak
A vacuum leak has the greatest proportional effect at idle when airflow is low, driving fuel trims positive.
Question 3: When diagnosing a P0301 (cylinder 1 misfire), the technician should FIRST:
- Replace all spark plugs
- Verify the misfire follows the cylinder by swapping coil/injector (Correct answer)
- Replace the ECM
- Flush the cooling system
Correct answer: Verify the misfire follows the cylinder by swapping coil/injector
Swapping components to a different cylinder shows whether the fault moves, isolating coil/injector versus a mechanical issue.
Question 4: A relative compression test using a current clamp on the starter is useful because it:
- Measures coolant temperature
- Identifies a weak cylinder without removing spark plugs (Correct answer)
- Tests the charging system
- Calibrates the MAF
Correct answer: Identifies a weak cylinder without removing spark plugs
Cranking current variation reveals a low-compression cylinder quickly without disassembly.
Question 5: A MAF sensor reading lower than expected grams-per-second at wide-open throttle will typically cause:
- A rich condition and black smoke
- A lean condition and possible hesitation (Correct answer)
- Higher idle speed
- Overcharging
Correct answer: A lean condition and possible hesitation
An underreporting MAF tells the ECM less air is entering, so it commands less fuel, creating a lean condition.
Question 6: Catalytic converter efficiency is best evaluated by comparing:
- Upstream and downstream O2 sensor activity (Correct answer)
- Battery voltage to alternator output
- Fuel pressure to vacuum
- Intake and exhaust valve timing
Correct answer: Upstream and downstream O2 sensor activity
A good converter stores oxygen, so the downstream sensor stays relatively steady compared to the switching upstream sensor.
Question 7: A P0420 code most directly indicates:
- EGR flow insufficient
- Catalyst system efficiency below threshold (bank 1) (Correct answer)
- EVAP large leak
- Camshaft position correlation
Correct answer: Catalyst system efficiency below threshold (bank 1)
P0420 reports that bank 1 catalyst efficiency has dropped below the calibrated threshold.
ASE Advanced Engine Performance Specialist 2
A wide-band (air/fuel ratio) oxygen sensor differs from a conventional narrow-band sensor primarily because it can: