ASE G1 Auto Maintenance and Light RepairAutomatic Transmission/TransaxleHard
A vehicle with an automatic transmission has a complaint of a buzzing or whining noise coming from the transmission area, particularly noticeable at idle in Park or Neutral. The noise changes pitch with engine RPM. What is the most likely source of this noise?
- AA worn differential bearing.
- BA faulty transmission output shaft speed sensor.
- CA failing transmission fluid pump.
- DA loose torque converter bolt.
Show answer & explanationAnswer & explanation
Correct answer: C. A failing transmission fluid pump.
A buzzing or whining noise that changes with engine RPM, especially noticeable at idle in Park or Neutral, is highly indicative of a failing transmission fluid pump. The pump is constantly operating when the engine is running to circulate fluid and build pressure. Worn pump components (e.g., gears, vanes, or bushings) can create such noises, which are often more prominent when not under load.
Why the other options are wrong
- A. Worn differential bearings typically cause noise that changes with road speed and cornering, not engine RPM at idle in Park/Neutral.
- B. A faulty output shaft speed sensor is an electrical component and would not generate mechanical noise; it would cause shifting issues.
- D. A loose torque converter bolt would typically cause a metallic 'clunking' or 'ticking' sound, especially when shifting or under load, not a continuous whine/buzz.
Failing Transmission Pump Noise
A buzzing or whining noise from the transmission that changes with engine RPM, particularly audible at idle in Park or Neutral, often indicates a failing transmission fluid pump.
- Pump operates continuously with engine.
- Worn internal components cause noise.
- Noise is often louder when not under load.
Memory trick: Whine at idle? The pump's design is getting wild.