ASE Exhaust Systems Specialist 3 — Questions and Answers
Question 1: A downstream oxygen sensor voltage switches rapidly like the upstream sensor. What does this indicate?
- The converter is operating efficiently
- The catalytic converter may be failing (Correct answer)
- The engine is cold
- The fuel pump is weak
Correct answer: The catalytic converter may be failing
An efficient converter produces a steady downstream signal; rapid switching suggests reduced converter efficiency.
Question 2: When welding a new section of exhaust pipe, why should the technician avoid welding near rubber hangers and fuel lines?
- Welding improves rubber durability
- Heat can ignite or damage nearby flammable components (Correct answer)
- It changes exhaust tone
- It voids the O2 sensor calibration
Correct answer: Heat can ignite or damage nearby flammable components
Welding heat can melt rubber hangers and ignite fuel, so flammable components must be protected or removed.
Question 3: A P0420 diagnostic trouble code typically indicates what?
- Catalyst efficiency below threshold (Bank 1) (Correct answer)
- Mass airflow sensor failure
- Misfire on cylinder 1
- EVAP leak
Correct answer: Catalyst efficiency below threshold (Bank 1)
P0420 signals the catalyst system efficiency on Bank 1 has dropped below the required threshold.
Question 4: Which exhaust component is specifically designed to cancel certain sound frequencies through wave interference?
- Catalytic converter
- Resonator (Correct answer)
- Exhaust manifold
- Oxygen sensor
Correct answer: Resonator
A resonator uses chamber geometry to cancel specific drone frequencies via wave interference.
Question 5: Before condemning a catalytic converter for a P0420 code, the technician should FIRST verify what?
- Tire pressure
- There are no exhaust leaks and the O2 sensors are functioning correctly (Correct answer)
- The battery state of charge
- The transmission fluid level
Correct answer: There are no exhaust leaks and the O2 sensors are functioning correctly
Exhaust leaks and faulty O2 sensors can falsely trigger P0420, so they must be ruled out first.
Question 6: What is a common symptom of a severely clogged catalytic converter?
- Improved fuel economy
- Loss of power and poor high-speed performance (Correct answer)
- Louder exhaust note
- Cold engine starting issues only
Correct answer: Loss of power and poor high-speed performance
A clogged converter restricts flow, causing power loss especially at higher engine speeds.
Question 7: Why must a torque wrench be used when installing oxygen sensors and exhaust flange bolts?
- To prevent thread galling and ensure proper sealing without distortion (Correct answer)
- To increase exhaust temperature
- To improve converter efficiency
- To set ignition timing
Correct answer: To prevent thread galling and ensure proper sealing without distortion
Proper torque prevents thread damage, leaks, and flange distortion from over- or under-tightening.
ASE Exhaust Systems Specialist 3
A downstream oxygen sensor voltage switches rapidly like the upstream sensor.
What does this indicate?