Notes On Alternator Functional Check
- With ignition on and engine off, ELECTRICAL PROBLEM light should be on.
- If the ELECTRICAL PROBLEM light is on with the engine running, see TELLTALE LIGHT DIAGNOSIS.
- Always diagnose Codes B410, B411 and B412 before performing alternator functional check. The trouble code charts will check the BCM's ability to detect alternator faults and to control alternator operation.
- This step checks for alternator overcharging of battery. Alternator overcharging of the battery may be accompanied by Code B412 (History or Current). Code B410 may also be set. Visual signs of battery overcharge may include electrolyte leakage from battery vents or low electrolyte level (indicated by Yellow battery "eye" or seen through side of battery case).
- This step checks for proper alternator current output. Alternator output less than 90 percent of rated output at 2000 RPM may result in undercharging of battery. Alternator undercharging of battery may be accompanied by Code B411 (History or Current) and ELECTRICAL PROBLEM light in instrument cluster being turned on. Code B410 may also be set.
Courtesy of GENERAL MOTORS CORP.