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

I was trying out some HID kits the other day, which I did not end up using. In the process I got a "charging system failure" notice on the DIC. I swithched to the battery voltage readout which reads around 27 volts with the engine running. I promptly shut the car off and it still reads 19 volts without the engine running. I checked the battery with a DMM and it read a normal 12 volts off and 14 volts running, which makes me think that something in the car's electronics is registering the voltage wrong. What sends the voltage reading to the DIC? I know there is a battery current sensor on the ground wire by the battery but is there a voltage sensor somewhere or is it in the ECM? Has anyone seen this before? Any suggestions? I have no electronic mods on the car, I am not using the HID kit, and I don't have any accessories installed.

check what voltages is coming out of the alt with it running, should be 14v~. There not built to run that high. Unplug the battery ground to reset the system. what year car is it? the 05 in you sig?

inside the alt is a voltage regulator, it maybe bad.

seems its still charging properly tho, being 12 off, and 14 running. those are good numbers.

Yes it is my 05, everything looks good on my multimeter, it is just that the readout on the DIC is reading high and giving a failure. The actual voltage is good. I tried unhooking the battery, it made no difference.

how long did you take battery off for

Have you re router the clamp near the battery terminals?

I took the battery off for roughly 30 mins. New information though, there is a small black wire with a white tracer connected to the negative battery lead with a connector just below the current sensor. The wire in question is not connected to the current sensor, it just goes through it. If I disconnect that wire the voltage reading goes back to normal but it gives a service vehicle light. Does anyone know what that wire goes to?

pic of said wire would really help out.

It got dark on me, I'll try to get one tomorrow if it isn't pouring rain. There are only 3 wires on the negative battery terminal, the other two are heavy gauge, this one is small like an 18 gauge and it disappears into the wiring harness just after the connector I mentioned.

After some research I found out that the wire is a ground lead directly to the BCM. Everything is pointing to a bad BCM. Anyone have experience with this and know what all is involved? Will I have to get it programmed by a dealer?

Have you tried a different DIC. Have you checked the voltage at the DIC plug? I can go bring up a diagram real quick.

To your other question yes a new bcm must be programmed with a tech2. A used bcm will not work. (vin locked, and also can have option configuration errors)

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Looks like it's data. Has a 12v source you could check voltage going in. A scanner like a tech2 could show what the bcm is seeing. The dic is either bad or the bcm is commanding those values. Any codes or weird lights coming on? Example abs or random dummy lights? Because at those voltages the car won't run. It actually be likely to see several bad modules caused by such a spike.

I'd put money on a bad DIC but if the bcm is bad (which if it were you should see other weird things happening as well like no power door locks or lighting issues etc) Can you communicate with the bcm?.
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Edit that's for an 04. Let me check 05.. Okay Diagram shows the wiring is the same for the different years.

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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.

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.

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.