I have a 2006 Gmc 1500 and every one in awhile the Battery light on the dash stays on and the "P" stays lite on the transmission indicator. The battery will be dead the next day. What's the problem?
I think you should buy a new one.
Sounds like either the alternator has a diode getting ready to fail or the BCM is not turning off the charge circuit when you turn off the key. The problem is catching it doing this, if it does try electrically disconnecting the alternator and see if both the lights go out, do NOT disconnect the battery or you will create more problems. if both lights go out then replace the alternator, if they don't then take it to a shop you trust and have the system checked out, it could be the BCM, but you can't just condemn without further testing. Maybe it just needs reflashing. HTH
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