I have a 2002 Pontiac grand prix SE 3.1 (200,000 miles). I have just installed the THIRD new alternator in less than 30 days. The battery is about 60 days old and I've had it checked multiple times to make sure I didn't get a bad battery. Everything checks out fine on the battery. I've tested each alternator and I'm getting some crazy results at times. 1st new alternator: I installed it and everything was fine for about 3 days. Then the battery light came on. I put a volt meter on and it was outputting 5.4 volts. I took it back and got the. 2nd new alternator: I installed it and it was outputting 21 volts! I thought perhaps my tester was bad so I used a different tester. Still got the same results. I took the car to the parts store and had them test it. By the time I got there the alternator was putting out 14.7 volts. I also tested it again with my tester to make sure I didn't have two bad testers. I got the same results as the parts store so my testers are fine. About 14 days later the battery light came on. I tested it and was getting about 6.4 volts. Took the car back to the parts store and they tested it again. They got the same results I did so they gave me another new alternator. 3rd alternator: I installed it yesterday. Additionally, I installed a new harmonic balancer and the crankshaft sensor. Everything went off without a hitch. I tested the new alternator and it was putting out 14.4 volts. I took the car to the parts store to return the 2nd alternator and get my money back. I had them bench test it to make sure it was bad and it was. It was putting out about 6 volts. I drove back home retested everything again and the output was 13.5 to 13.8. Went out to dinner later that night and the battery light came on. Tested it again and sure enough it was putting out 6.2 volts. This time the light is on for a few minutes then back off, then back on, etc. I'm at a loss here! The first alternator I bought was NEW (not rebuilt). The other two were rebuilt. I've had the battery checked multiple times. I've cleaner the battery terminals and cables repeated (not that they needed it). There was/is no corrosion on either cable/terminal. I DID have a high-end audio system with separate amps and such. I disconnected it after the 2nd alternator thinking that maybe I had something going on there but that obviously didn't help.
UPDATE: Since I posted this question originally I did some further testing. I connected a 10 gauge wire directly from the alternator post to the positive battery post. The voltage is now pretty stable from 14.7 volts (when I first started the car) to 13.5 volts after it ran for about 10-15 minutes. Also, I checked both fusible links that are down near the starter. Both look good with no melting or corrosion or cracking.
I disconnected the 10 gauge wire from the battery to the alternator that I added and waited about an hour. I tested the car again WITHOUT the 10 gauge wire and got 6.4 volts. I reconnected the 10 gauge wire again and all the readings were normal.
However, I'm now getting a P0502 code which I have never gotten before. That is the only code in the system.
Any ideas on what could be wrong with the alternator/charging and now the P0502 code?
Thanks in advance for any insight! Jack
Monday, February 25th, 2013 AT 10:14 PM