Body Control Module... Which wires are which?
09-13-2011, 10:02 PM
#1
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Body Control Module... Which wires are which? So I'm having issues starting after relocating my battery to the rear. Power comes on and voltage reads good all across the power wire as well as the starter and fuse panel wires. But when I turn the key I get nothing, no clicking, no nothing. Just have my security light on the dash flashing the hell out of me every time I open the door. Someone said that this is likely an issue with the anti-theft system in the BCM. They said that I should cut the starter relay ground wire and ground it directly, bypassing the BCM. I assume they mean ground it directly to the car. I have two questions...
1. Which wire going to the BCM is the starter relay ground wire? My God there's a lot of wires going to this beast.
2. Do you think this will work? More specifically, has anyone had to do this before and have it work?
1. Which wire going to the BCM is the starter relay ground wire? My God there's a lot of wires going to this beast.
2. Do you think this will work? More specifically, has anyone had to do this before and have it work?
09-14-2011, 07:31 AM
#2
This question has a lot more detail than the one you posted in the BCM solder fix thread so the answer there is incomplete.
Someone has given you only half-assed advice. The VATS system in the BCM actually has two safeguards against vehicle theft. One is that it disables the starter relay by removing the ground to the relay coil. That can be bypassed by grounding the yellow with black wire in position C12 of the 32-pin blue connector at the BCM. The other is that it disables the fuel enable signal to the PCM. This can be programmed out of the PCM by a tuner.
It's actually simpler to bypass the entire VATS system by substituting the correct resistance in the sensor wires so that the key resistor pellet doesn't matter.
However, a couple of points you mentioned make me wonder whether there is some other problem here. The flashing security light indicates that the BCM is not seeing any key pellet at all (there is an open circuit or infinite resistance between the two sensor wires). Are you sure the wires are plugged in under the steering column?
The other thing is it sounds like you get nothing when you turn the ignition to the on position. The VATS system affects the starter and fuel enable but has nothing to do with the normal ignition controlled circuits. You should still have all your accessories working (radio, windows, turn signals, HVAC, etc.) and the instrument panel warning lights should still go on for several seconds (test cycle). If not then you have a problem with your ignition - either the switch or its wiring - that is unrelated to the BCM.
BTW, here is the same link to the BCM connector schematics I posted in the other thread: https://ls1tech.com/forums/11633365-post7.html
Someone has given you only half-assed advice. The VATS system in the BCM actually has two safeguards against vehicle theft. One is that it disables the starter relay by removing the ground to the relay coil. That can be bypassed by grounding the yellow with black wire in position C12 of the 32-pin blue connector at the BCM. The other is that it disables the fuel enable signal to the PCM. This can be programmed out of the PCM by a tuner.
It's actually simpler to bypass the entire VATS system by substituting the correct resistance in the sensor wires so that the key resistor pellet doesn't matter.
However, a couple of points you mentioned make me wonder whether there is some other problem here. The flashing security light indicates that the BCM is not seeing any key pellet at all (there is an open circuit or infinite resistance between the two sensor wires). Are you sure the wires are plugged in under the steering column?
The other thing is it sounds like you get nothing when you turn the ignition to the on position. The VATS system affects the starter and fuel enable but has nothing to do with the normal ignition controlled circuits. You should still have all your accessories working (radio, windows, turn signals, HVAC, etc.) and the instrument panel warning lights should still go on for several seconds (test cycle). If not then you have a problem with your ignition - either the switch or its wiring - that is unrelated to the BCM.
BTW, here is the same link to the BCM connector schematics I posted in the other thread: https://ls1tech.com/forums/11633365-post7.html
09-14-2011, 11:33 AM
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Thank you for the link! I should have clarified... when I turn the key on I still have all power and accessories (radio, windows, etc...) but when I try to turn it over, nothing happens. The starter does not click at all. The fuel pump also primes as normal.
I didn't touch anything so I would think so. The light flashes when the door is open and the key is not in the ignition and stays on when the key is in and the door is left open. Whenever the door is closed, the light goes off.
I see the wire in C12 is the security lamp control. I assume the yellow wire is the one that runs to the relay at the fuse box but where is it at the BCM? Looking at the schematic it looks like C11 but just double checking. And if I do this will I have to disable VATS entirely?
Thanks for the help man, this damn thing literally has me sick right now.
Are you sure the wires are plugged in under the steering column?
That can be bypassed by grounding the yellow with black wire in position C12 of the 32-pin blue connector at the BCM.
Thanks for the help man, this damn thing literally has me sick right now.
09-14-2011, 12:23 PM
#4
I see the wire in C12 is the security lamp control. I assume the yellow wire is the one that runs to the relay at the fuse box but where is it at the BCM? Looking at the schematic it looks like C11 but just double checking. And if I do this will I have to disable VATS entirely?
Connecting the yellow/black wire to ground solves only half the problem. It will remove the starter from VATS control but still leaves you with a missing fuel enable signal from the BCM to the PCM. So the car will start and then die of fuel starvation after a few seconds. Bypassing VATS is the best way to resolve the problem.
09-14-2011, 12:45 PM
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Sorry, my mistake. The yellow/black wire is the one that goes from the starter relay coil in Junction Block #2 under the hood to pin C11 in the blue connector at the BCM. I mistyped C12 in the previous post.
Connecting the yellow/black wire to ground solves only half the problem. It will remove the starter from VATS control but still leaves you with a missing fuel enable signal from the BCM to the PCM. So the car will start and then die of fuel starvation after a few seconds. Bypassing VATS is the best way to resolve the problem.
Connecting the yellow/black wire to ground solves only half the problem. It will remove the starter from VATS control but still leaves you with a missing fuel enable signal from the BCM to the PCM. So the car will start and then die of fuel starvation after a few seconds. Bypassing VATS is the best way to resolve the problem.
09-14-2011, 01:42 PM
#6
Assuming this is a factory alarm (which might be a very big assumption), you can program it not to arm so you can eliminate it as a cause of your starting problem. Instructions are in the owner's manual and posted here. But if it is a factory alarm system then I doubt it is causing your problem - I suspect the problem is electrical rather than electronic and some good old-fashioned diagnostic tracing will be necessary.
If it is an aftermarket alarm then all bets are off - it could easily cause your symptoms and be very difficult to correct.
09-14-2011, 03:16 PM
#7
So I'm having issues starting after relocating my battery to the rear. Power comes on and voltage reads good all across the power wire as well as the starter and fuse panel wires. But when I turn the key I get nothing, no clicking, no nothing. Just have my security light on the dash flashing the hell out of me every time I open the door. Someone said that this is likely an issue with the anti-theft system in the BCM. They said that I should cut the starter relay ground wire and ground it directly, bypassing the BCM. I assume they mean ground it directly to the car. I have two questions...
1. Which wire going to the BCM is the starter relay ground wire? My God there's a lot of wires going to this beast.
2. Do you think this will work? More specifically, has anyone had to do this before and have it work?
1. Which wire going to the BCM is the starter relay ground wire? My God there's a lot of wires going to this beast.
2. Do you think this will work? More specifically, has anyone had to do this before and have it work?
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09-14-2011, 11:18 PM
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WhiteBird...
Thank you so much for all the help. It is a factory alarm system. I think I'll give shutting it down a try. I noticed the shock sensor deal in the rear quarter when I relocated the battery as well. Having a guy come over this weekend and hopefully we can trace this little bastard down. Electrical gremlins are without a doubt the biggest PITA of all time.
Yup, worked fine for a couple of weeks. Turned over a bit harder than it did when it was up front but I read that this was a common problem. Then all of a sudden one day it just stopped turning over entirely.
Thank you so much for all the help. It is a factory alarm system. I think I'll give shutting it down a try. I noticed the shock sensor deal in the rear quarter when I relocated the battery as well. Having a guy come over this weekend and hopefully we can trace this little bastard down. Electrical gremlins are without a doubt the biggest PITA of all time.
after you relocated battery to rear did it ever work?
09-16-2011, 12:05 PM
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Well I disabled the alarm system and still nothing. Still 12.2 volts from battery to distribution block to starter all the way around. When I try to turn it over voltage to starter goes down to 11.5 or so (which I believe is normal). Guess it's time to put on the detective hat this weekend.
