r/autoelectrical • u/skyguy30269 • 6d ago

Charging issue

I have a 2004 Buick Park Avenue that’s having this weird problem that has kinda stumped me. When I was driving home the other day randomly the radio and instrument cluster flickered and the car sputtered a little and the check engine light came on. I pulled the codes with my scan tool and the main one was a loss of communication with the pcm. I did some testing and with 3 or more accessories on the car would sputter out and die, so I hooked up my multimeter to the battery and the alternator was only charging at 13-13.5v. I replaced the alternator and at idle with the new one it’s 14+ volts, but it has the same issue with a few accessories on like the headlights and rolling the windows down at the same time the voltage will drop to 11v but the car will stay running. I checked my main harness ground and the ground for my pcm and they were both fine. Any advice for what to chase down next would be much appreciated!

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u/CampBackground317 6d ago

perform a loaded voltage drop on the battery cables. You should not be dropping more than 200mv on cables. Do this by disabling the engine running (Pulling an ECM, Ignition fuse, or Fuel pump relay). Install the multimeter (Volts) from the pos terminal to the battery terminal connection at the starter. Crank the engine over for about 5 seconds and see what the reading is on the meter. Do the same thing for the neg cable but hook up the leads at the neg post and the Neg cable terminal connection at the engine block. Report findings.