Abnormal engine noise of 2007 GAC Toyota Camry
2026-04-09
Background
Vehicle Model: 2007 GAC Toyota Camry
Mileage: 66,915 km
Fault Phenomenon
Abnormal noise occurs from the engine, suspected to be bearing noise. Detailed inspection via mechanic's stethoscope reveals loud noise originating from the alternator.
The stethoscope confirms the abnormal noise comes from the alternator (See Figure 1). The alternator was then removed for disassembly inspection.
Repair Solution
Rotate the alternator rotor by hand; it spins smoothly with no bearing looseness detected. Remove the rear cover of the alternator and disassemble to inspect the carbon brushes. No defects are found: the carbon cores retain ample length, and the rotor slip rings show no abnormal wear (See Figure 2).
Repair Plan
A functional alternator was sourced, its rotor and bearings removed and installed onto the faulty noisy alternator. The alternator was reassembled and a vehicle test run was conducted after startup, yet the abnormal noise persisted. The repair work hit an impasse at this point.
The alternator was disassembled again for thorough inspection; no interference between the rotor and stator was observed. It suddenly occurred to the technician that the electrical components had not yet been checked. A multimeter was used to measure the continuity resistance of the rotor winding, which read normal. When measuring the resistance of the stator winding, abnormal readings were obtained with incorrect insulation resistance to ground.
Individual windings were tested one by one for ground resistance, revealing excessively low voltage drop. It was suspected that one or more diodes in the rectifier bridge had broken down (See Figure 3).
Measure the voltage drop of the windings against the positive terminal again; all readings are normal. For this reason, the alternator can still generate electricity and the charging warning light stays off, yet its power output is severely insufficient.
To verify the rectifier bridge fault, reassemble the alternator and measure the battery voltage after starting the engine. The voltage indeed fails to reach the standard level, only reading 12.5 V. Even when revving the engine up to 2000 r/min, the voltage remains unchanged.
Since the rectifier module is not sold as a separate spare part, the complete alternator assembly is replaced, and the fault is eliminated.
