Charging system issue

BIGFOOT1999

MEMBER
2001 PONTIAC GRAND AM
2.4L
4 CYL
FWD
AUTOMATIC
220,000 MILES

SE 2.4L, 4 cylinder car. Had a bad alternator. Replaced alternator and battery. It all worked fine for about 2 days. Then more issues.

It runs fine for about 5-10 minutes. Battery voltage with alternator charging at 14.5 - 14.6 volts. Then the voltage drops to 12.5 and continues to drop. I have checked all the ground points that I could find on the car, no loose terminal connections to the battery, fusible link is intact. Battery checks out good. Fuses are good.

Does anyone know what could possibly be causing my alternator to go from working perfectly to not working at all in 5-10 minutes. Im clearly missing something here. Any help to point me in the right direction would be greatly appreciated.

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

There are a number of things left that can cause this but due to the fact that the system operates properly then it stops charging points to either a control issue or a wiring issue that is caused by heat.

Just to make sure we are on the same page make sure this is how you are testing the alternator:

https://youtu.be/Z-p4dMJUpUw

If it is, then we need to check the voltage on terminal B when this is operating properly and then when the voltage drops. This is the field control wire so if the PCM is commanding the regulator to drop the voltage then the PCM is most likely the issue.

https://www.2carpros.com/articles/how-to-check-wiring

Please see the wiring diagram below and let us know what you find.

Thanks

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