2003 impala 3800

my battery drains if i leave it hooked up over night: and the gauges will sometimes start to click and flicker and move when the key is out of the ignition
: i have changed batteries 3 times in 1 yr and checked the alternator, everything is fine, i’m tired of disconnecting my battery every night before bedtime…

You have a “parasitic drain”. Here is a video to help you find it:

Open the drivers door and open the fuse box on the side of the dash and remove the 10 AMP fuse labled, CLSTR/BCM. If the battery doesn’t drain overnight the problem is likely with the Body Control Module.


Tester, Have You Seen Many BCMs With These Symptoms On Chevrolets, GM Cars, Or On Cars In General ?

Pardon my automotive electrical ignorance, but say you pull that fuse and the battery stays up, and let’s say that some electrical item that is controlled through the BCM has a fault, how do you know it’s the BCM that’s bad and not the one item with the fault ?


Well, if you remove power from the BCM the components that are contolled thru the BCM can’t function.


Thanks. Are You Saying That The Problem Is Then The BCM Or You’ll Know That It Is Something Controlled Through It And Further Diagnoses Will Determine Which Something It Is ?


And yes. I’ve seen this happen on all kinds of vehicles.

I once had a Lincoln come in where nobody could figure out what was causing the battery to drain down. The owner dropped it off one night and left. While it was sitting in the shop I went out to do something at the bench. Now the shop is dark except for the lights over the bench. When I finished at the bench I turned around and the interior lights of the Lincoln were on. As walked towards the car the lights dimmed back down. I stopped and waited and the lights came back on. I waited and after about 10 seconds the lights dimmed back down. So I went and sat on a stool and watched the car. It was random. The lights would come on for 10 minutes and shut off, or stay off for 20 minutes before coming back on.

The problem was caused from a faulty Body Control Module.


Thanks, Again.

I’ve only had one experience with a BCM. I installed a used one (30 bucks) and solved a couple of electrical prolems (they surfaced at two different times and pointed toward a BCM - gas gauge/wipers - phantoms). The dealer wanted 800 bucks and impound the car til it arrived.

I found out why the impound procedure, after I installed the used BCM. My odometer reading changed to that of the salvage yard car !

Taking the cover off the faulty BCM revealed some suspicious looking corrosion on the circuit board near the big connector.

I’ve got to get a scanner that will read body codes , ABS, and SRS, besides just ECM codes. I need to spend about $300, I think.


No way! You can’t buy a scanner for $300.00 that’ll pull ABS, SRS. and BCM codes.

OBDII is mandated by the EPA as a standard protocol for emissions. But when it comes to all other systems each manufacturer has it’s own protocol. So not only will you need the base scanner, but also all the different programs for the scanner to communicate with all the different protocols.


Tester, Here’s One I’ve Been Looking At For A While.
I don’t see BCM on it. It won’t retrieve BCM codes ?
What am I missing ? Can it do ECM and ABS and SRS on GM and Chryslers ?



No BCM Capablity. And it says on MOST Ford, GM, Chrysler, Honda, Toyota vehicles not ALL. What does most mean? And up to what year?


@commonsenseanswer it sounds like you want a professional level scanner.

I have a Snap On Solus Pro. I bought it a few years back. Price was $3800. There’s a newer version out now. Price is roughly the same. OTC also has different models. Also not dirt cheap.

Bottom line:

If you want to do PCM, ABS, SRS, BCM, OCS, etc., you’re going to have to spend serious bucks.