Thread: Volt gauge reading high, "charging system failure"

Originally Posted by Aeroheadcww

I went through the BCM harness and checked the 12v source wires and they all read okay. Reading the diagnostic info in eSI it says to check between the sources and their corresponding ground but it does not say which grounds correspond to which inputs. Anyone have any info on that? Also, there is a 12v reference lead that goes to the ignition switch from the bcm, I am confused about that circuit but I am guessing the car wouldn't be running if it was bad.

Sorry to bump an old thread but I'm having the identical issue as the OP. The car runs/starts fine and all electronics are fine. I am also getting this charging system failure issue on my 2005 Grand Prix GT. I've cleaned my battery terminals, checked voltage at battery and alternator, checked OBD II voltage and all checks out fine when off or even on a load. All of the local auto part stores say everything is fine with my battery and alternator. The battery was replaced a few years ago and the alternator is original.

Just as the OP said, when I unplug this mystery black wire with a white line on it that comes right from the ground wires on the battery terminal, the voltage will read correct on the DIC but I get a service vehicle soon message. When I plug it back in, the voltage on the DIC shoots up to ~18-25 volts and says charging system failure. When checked with my DMM, it shows a proper 12.8-14.5 volts.

I've been troubleshooting this for 2 weeks and want to figure it out. I am beyond stumped and want to get this taken care of. Any help or advice is appreciated!

Originally Posted by Aeroheadcww

This ended up being a bad BCM. I bought one on Amazon (http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1). The replacement part numbers were changed a few times but the final part number for mine was ACDelco 15942206, which was a generic replacement for many GM cars that has to be programmed by a dealer. I replaced it myself, and after you go through the security relearn procedure you can drive it to the dealer. My dealer charged around $80 for the reprogram, and the only issue I have with it is that the door locks cycle twice when you put the car in reverse instead of just locking like it is supposed to.

The dealer told me that it was my alternator, and assured me of that. They were wrong, and I spent $200 on an alternator that I don't need. I am sure that they would have charged me a lot more and came up with the wrong diagnosis again and again if I had left it up to them. Beware of lazy mechanics, its hard to find one that will actually research and investigate an issue like this.

First off, thanks for your reply as I've searched in many areas and you're the only one to have the same issues. That being said, did you change your BCM due to it being an annoying false alarm ot did you run into other issues? More recently, I'm getting the "service vehicle soon" error on my DIC. I only got this error before when I unplugged the small ground line near the battery. It seems to be an issue related to the ground either on the BCM or at the main location on the vehicle.

How hard was it do pop the BCM in and re-learn? Any input is greatly appreciated as every mechanic has wrongly diagnosed it. Really trying to avoid the stealership.

Originally Posted by Aeroheadcww

Unfortunately you cant avoid the stealership on this one. The bcm has to be programmed to your car. I changed mine because i was having charging issues that showed up intermittantly. I had to jump the car off a couple of times. It was easy to change, its under the driver side dash. The security relearn you can do a quick search for, its no big deal. Expect tons of errors until you get it programmed.

Thank again!

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