ASE - Automotive Service Excellence Practice Test #4 1 — Questions and Answers
Question 1: A technician is performing a compression test on a 4-cylinder engine. Cylinders 2 and 3 both show low compression readings. What is the MOST likely cause?
- Worn piston rings on both cylinders
- A blown head gasket between cylinders 2 and 3 (Correct answer)
- Faulty intake valves on cylinders 2 and 3
- Low engine oil pressure
Correct answer: A blown head gasket between cylinders 2 and 3
Adjacent cylinders with simultaneous low compression strongly indicate a blown head gasket between those cylinders, allowing combustion pressure to leak between them. Worn rings would typically show improvement with a wet compression test, and valve problems rarely affect two adjacent cylinders simultaneously in the same pattern.
Question 2: A customer complains of a vibration felt in the steering wheel only during braking. The vibration is not present during normal driving. Technician A says the front brake rotors are likely warped. Technician B says the front wheel bearings are worn. Who is correct?
- Technician A only (Correct answer)
- Technician B only
- Both Technician A and Technician B
- Neither Technician A nor Technician B
Correct answer: Technician A only
Steering wheel vibration that occurs only during braking is a classic symptom of warped or thickness-variation front rotors. Warped rotors cause pedal pulsation and steering shake specifically under braking force. Worn wheel bearings typically produce noise and vibration during driving or cornering, not exclusively during braking.
Question 3: A vehicle's OBD-II system sets a P0420 code (Catalyst System Efficiency Below Threshold, Bank 1). Before condemning the catalytic converter, what should the technician inspect FIRST?
- The oxygen sensor heater circuit
- Exhaust leaks upstream of the downstream oxygen sensor (Correct answer)
- The fuel injectors for proper spray pattern
- The EGR valve operation
Correct answer: Exhaust leaks upstream of the downstream oxygen sensor
An exhaust leak upstream of the downstream (post-cat) oxygen sensor can introduce outside air, causing the sensor to read falsely lean and mimicking a failing catalyst. This is a common misdiagnosis trigger and should be eliminated before replacing an expensive catalytic converter. The downstream O2 sensor's readings depend entirely on exhaust gas composition reaching it.
Question 4: When measuring battery state of charge with a hydrometer on a conventional flooded lead-acid battery, a technician finds one cell reads 1.175 specific gravity while the remaining five cells read approximately 1.265. What does this indicate?
- The battery needs to be fully recharged before testing
- The battery is fully charged and ready for service
- One cell has a dead short or internal failure (Correct answer)
- The electrolyte level is low in all cells
Correct answer: One cell has a dead short or internal failure
A single cell reading significantly lower (more than 0.050) than the others indicates that cell has an internal short circuit or plate failure and cannot hold a charge. A battery with one dead cell will fail under load even if the other cells appear healthy, and the battery must be replaced. A low charge condition would affect all cells relatively equally.
Question 5: A technician is diagnosing a vehicle with a complaint of hard starting when the engine is hot, but normal starting when cold. The engine cranks normally. What is the MOST likely cause?
- A faulty coolant temperature sensor sending a cold signal
- Fuel pressure dropping due to a leaking fuel pressure regulator or injectors (hot soak) (Correct answer)
- A weak battery that cannot supply sufficient cranking amperage
- A clogged fuel filter restricting flow at idle
Correct answer: Fuel pressure dropping due to a leaking fuel pressure regulator or injectors (hot soak)
Hot soak hard starting is a classic symptom of fuel pressure bleed-down after shutdown. A leaking fuel pressure regulator or injectors allow fuel rail pressure to drop while the engine is off and hot. When restarted, the engine must crank longer to rebuild pressure before fuel can atomize properly. Cold starts are unaffected because pressure holds during the overnight soak.
Question 6: A rear-wheel-drive vehicle pulls strongly to the left during hard acceleration but tracks straight during coasting. Which condition is the MOST likely cause?
- Unequal tire pressure between the left and right rear tires
- A broken or sagged rear leaf spring on the left side
- Excessive positive caster on the left front wheel
- Rear axle housing torque wrap causing pinion angle change under load (Correct answer)
Correct answer: Rear axle housing torque wrap causing pinion angle change under load
Torque steer during acceleration on a rear-wheel-drive vehicle is often caused by the axle housing rotating (wrapping) under driving torque, which changes the pinion angle and can shift lateral forces. This only occurs under power because the drivetrain torque reaction is what causes the wrap. A broken spring would cause a side-to-side height difference visible at rest, and tire pressure or caster issues affect all driving conditions, not exclusively acceleration.
ASE - Automotive Service Excellence Practice Test #4 1
A technician is performing a compression test on a 4-cylinder engine.
Cylinders 2 and 3 both show low compression readings.
What is the MOST likely cause?