Bad BCM?
Bad BCM? Just wondering about the bcm on the f cars. I have been having a problem that is much like a parasitic drain on my battery. Every couple days I find the car's battery dead. I have replaced the battery more than once , the alt twice, and cleaned all grounds that I could found. Had it load tested etc and tested for parasitc drains. Notihing. However when the passenger side door was locked with the keyless entry (remote) it seemed like the readings went all over. Ultimately though the system still goes to sleep after the designated 15 minutes like it should. So what's draining the battery or turning something on (waking up the bcm) at night? I'm at a loss here and figure it is either a bad BCM or a short somewhere (I really hope not 
) .
I had the key and igntion replaced at the dealership due to the security light being "on" all the time. I'm wondering if that is the problem? I read on this site somewhere that the bcm programs/locks to the resistance of the first key it is started with. If that is the case, then how does one reprogram the bcm correctly after a new key/cylinder has been added? I understand the bcm is VIN specific, so the dealership must have either: a) not bothered to reprogram the bcm for the new key (which I don't even know if the vehicle would even start in this case?) or
b) reprogrammed it but didn't realize the bcm is bad?
I'm lost here so any ideas would be great. I have read on here about almost everything to do with headlights, bcms, window motors, alternators, batterys, etc. and I'm still stuck.
Thanks.
) . I had the key and igntion replaced at the dealership due to the security light being "on" all the time. I'm wondering if that is the problem? I read on this site somewhere that the bcm programs/locks to the resistance of the first key it is started with. If that is the case, then how does one reprogram the bcm correctly after a new key/cylinder has been added? I understand the bcm is VIN specific, so the dealership must have either: a) not bothered to reprogram the bcm for the new key (which I don't even know if the vehicle would even start in this case?) or
b) reprogrammed it but didn't realize the bcm is bad?
I'm lost here so any ideas would be great. I have read on here about almost everything to do with headlights, bcms, window motors, alternators, batterys, etc. and I'm still stuck.
Thanks.
Could my Diablo tune have possibly messed up the bcm? I know this seems unlikely but I know the bcm controls rap, what controls the bcm? Does the pcm talk to the bcm, I am inclined to think not unfortunately.
Last edited by oddwraith; Feb 25, 2010 at 05:20 PM. Reason: speeling
when we replace those ignition cylinders and the keys we dont have to program them, we have a vats tester and we determine what the keys resistance and order a key that is the same resistance and cut it to fit the new ignition cylinder, your bcm could be the issue if you have only tested it once for the parasitic draw then you may not have seen it, sometimes you have to put the draw tester on, drive the vehicle and make sure you turn on all electronic components roll the windows up and down, play with the radio, pop the trunk open and close all the doors, etc... then test for a parasitic draw, at max you should only have about 25 mA of draw on the system, hope some of this helped.
Well we did check for draw trying various things as we did (like you mentioned above) and at that time we narrowed it to BCM or possibly passenger side door sensor. I have read about a bcm fix on here and am considering doing this myself. Thanks for ideas.
