2007 P71 battery boiling

This was the first thing i saw, like this fellow. https://youtu.be/EE7Ehm37za8 Then the battery light would come on once the power restored. I realized that was because the battery was overheating.

Put voltmeter on battery while running. Are you over 15 volts?

Also, check all your grounds. Main one is the battery negative but find the alternator ground, engine ground and body ground. A bad grounding wire will cause boil over. Have you tested your battery cables for voltage drop?

If all the physical grounds are good, you could have a bad PCM if this controls your voltage. Acts as your regulator.

I checked the cables for shorts and voltage, they are working correctly, the voltage is spuratic, when it fails. The car will work with no problems just like in the video. I also suspected a bad engine cooling fan, its only two years old, but if shorted, that could maybe cause power spikes and lows when it turns off and on. It will be interesting to see wjat the dealership says. I see a PMC can run $1200.

So the dealer verdict. A wire from the pcm to the alternator was shorting. He also changed the pigtail in the alternator which i thought had looked good, maybe the shorting beat it up. The wire was red, i saw a blog where a guy was saying a green wire was doing the same thing. 50 dollars to fix, 500 for labor, and tax. Kind of expensive but they troubleshot it in a hour and had it ready for pickup in 4. Prolly wiuld have taken me weeks to chase wire.

The harness says $836, which i would have done, but they dont make them anymore. Super easy to change, but couldnt get one. Would have been cost effective as compaired to paying almost 600 just for a fix.

Really i just hope this post helps someone else.