2001 Duramax Battery Problems
 

Hey guys,
My bro in law has a 2001 1 ton 4x4 duramax w/allison. His batteries were the factory set. They were getting slower and he charged them up last winter and again this week. So he replaced the batteries and brake controller lit up with no trailer on, clock on radio would flash when hitting brake pedal. So he unhooked the batteries thinking he needed to reset the computer. checked all fuses and all were good. Hooked batteries back up, All exterior lights came on with switch off and the key NOT in the ignition and the interior chime came on and brake cotroller said trailer was plugged in when it was not. And interior light relay got somhot he pulled it so not to burn something up. He did not touch a wrench to any ground when putting terminals back on and he had them hooked up right.
Do any of ya'll have any idea what could be the problem? he doesen't know what to do. Any and all ideas would be welcome!! thanks guys
ez

that's wierd. first thing that comes to mind is i'm wondering if that has or ever has had a remote start on the truck. i have seen those cause some really strange things over the years. if he bought it used i'd triple check under the driver's side of the dash for any aftermarket modules. i'd be really surprised not to find one in there somewhere. just for gits and shiggles i'd pop the cover off the junction box where the brake box plugs in and unplug it too just to see if it affects anything. i don't think it will though. it's to the left of the brake pedal, almost directly behind the parking brake pedal up against the firewall.

if all of that fails, remove the driver's side knee bolster trim from the dash. it's 2 7mm head screws on the bottom of the panel. then pull the trim around the instrument cluster. just pull the bottom of it out and the you can pull the knee bolster trimm off. just about 6-8 inches under the steering wheel you'll see 3 plugs sitting side by side in a module. that's the body control module or BCM. with the batteries disconnected unplug the 3 connectors from the BCM then reconnect the batteries. if all is good, go ahead and plug the BCM back in and see if it's still ok. sometimes BCM's will go into a loop/logic lock up and cause strange stuff to happen too.

Thanks chimpo! He bought it brand new and it has never had a aftermarket module even close to it! Also it is a really striped down model silverado, crank windows, am fm radio, manual locks, rubber floor, and stuff like that. I will have him check what you said and get back here to give a progress report! haha
ez

I am very shocked that his factory batteries lasted that long. Usually only get 3 years max out of them. The problem he is having is that the BCM has lost it's shut down memory. When the ignition key is turned off the BCM stores parameters in memory that are required for start up and then pulls them back up the next time the ignition key is turned on. Sounds like the BCM is no longer storing this information so when he turns the key back on it doesnt know what needs to be turned on or off. Did he charge the batteries while still connected to the truck? If he got a power spike then it may have fried the RAM in the BCM. It's possible that he could have the dealer reflash the BCM and it might correct the issue. If not, he's going to have to get a new BCM. Shouldnt have a problem finding one at a salvage yard and then reflashing it.

Thanks DD, I will let him know and see if we can figure it out!
ez

Tured out to be a screw in the trailer receptacle on the truck had a short in it! who knew!
ez

lol. unbelievable. hell of a time for coincidence!! glad you guys got it handled and thank you for posting the repair. i'm going to close the thread and move it to the bombers support section.