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I have a battery drain on my 04 malibu.
I search for the drain with a test light by pulling fuses until the light goes out. The j fuse labeled IBCM 1 cuts the light off but kills everything else as well. I really need this car. How do I find exactly what is killing my battery?
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Answers
What you need to do is:
1. charge up the battery and make sure it reads around 12.5 V with your volt-ohm meter (VOM meter)
2. Turn your VOM to the highest AMP setting (20 A? 10A)--start with that. Then hook up your VOM in series by disconnecting the NEGATIVE battery cable, not the positive one. So you are disconneting the negative cable, pulling it off the battery, and putting one lead of your VOM on the post and the other on the cable you took off.
3. OK, now you have to be sure that NOTHING is on, in the car. No doors open, no key in the ignition, no "proximity key" in your pocket.
4. Now you can read the amp draw, if any. Anything over 50 milliamps is a problem, If it's 50 ma or less, then you don't have a parasitic draw.
The fact that you have a draw on the BCM fuse makes me suspicious of your diagnosis, because on many modern cars, various modules need to "go to sleep" when you turn the car off, and this could take up to 1/2 hour. So you may find that if you leave your meter connected (and NEVER open the door with your meter connected, or you'll damage it !!), you may see the alleged amp draw go away by itself--or diminish perhaps.
Keep in mind you might have more than one fuse box in your car. Here again, if you have to go to a passenger compartment fuse box, DISCONNECT your meter before you open a door--then tape or block the door switch so that you don't send lots of current through your meter. If you can't immobilize the door switch, then get in the car, close the door and have a friend hook up the meter and put it on the windshield facing you as you pull more fuses.
You may be able to download a wiring diagram at www.BBbind.com.
So be sure you have a good strong battery. If your battery is defective, it will behave like a parasitic draw but that's a false diagnosis.
Short Answer--you can't solve this with a test light and without a wiring diagram.
Also, if you have any aftermarket gadget recently hooked up, like an alarm or stereo, that's your top suspect.