Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsCharging System Diagnosis and RepairEasy
A technician is diagnosing a vehicle with an illuminated battery light and a strong burning smell coming from the alternator. Upon inspection, the alternator pulley feels very loose and wobbly. What is the MOST likely cause?
- AOpen stator winding
- BWorn alternator bearings
- CFailed voltage regulator
- DShorted rectifier diode
Show answer & explanationAnswer & explanation
Correct answer: B. Worn alternator bearings
A loose and wobbly alternator pulley, combined with a burning smell, is a classic symptom of worn or failed alternator bearings. When bearings fail, they create excessive friction, heat (burning smell), and allow the rotor assembly (and thus the pulley) to move excessively, leading to noise and eventual alternator failure.
Why the other options are wrong
- A. An open stator winding would cause a loss of output and possibly overheating, but not mechanical looseness of the pulley.
- C. A failed voltage regulator primarily affects voltage output and wouldn't typically cause mechanical looseness or a burning smell from the bearings.
- D. A shorted rectifier diode causes AC ripple, heat, and reduced DC output, but not mechanical looseness of the pulley.
Alternator Bearing Failure
Malfunction of the internal bearings that support the alternator's rotor shaft, leading to mechanical noise, looseness, and eventual failure.
- Supports rotor shaft rotation.
- Failure causes noise and vibration.
- Can lead to pulley wobble and burning smell.
Memory trick: Wobble and Burn - Bearings are the Culprit, Learn!