Is there a way to bypass the BCM?
Is there a way to bypass the BCM? I'm not sure where this goes since and since I don't see an electrical forum, I thought this the best place for it.
I am being told of the horror stories that is the BCM. Is there a way to by pass it all together? I've been trying to read up on it, but I don't know a lot about electrical stuff. I mean this thing is scary... if I understand right, you can't get a replacement from GM and no one makes them, so when yours takes a complete ****, you're **** out of luck, or so my understanding is about this thing. Is this correct?
I am being told of the horror stories that is the BCM. Is there a way to by pass it all together? I've been trying to read up on it, but I don't know a lot about electrical stuff. I mean this thing is scary... if I understand right, you can't get a replacement from GM and no one makes them, so when yours takes a complete ****, you're **** out of luck, or so my understanding is about this thing. Is this correct?
Joined: Nov 2001
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From: Schiller Park, ILL Member: #317
I'm not sure what these "horror stories" are. Sometimes a solder point will crack on the circuit board, there is a thread about fixing that (simple soldering job). Outside of that, I don't really know of any other serious/common problems with the BCM. I've owned tons of GM cars that use these, some with lots of age/miles, never had a problem....and if I do, I'll just solder it back up and go about my life.
It's not something I'd loose any sleep over.
Here is the "fix" thread.....
https://ls1tech.com/forums/general-l...blems-fix.html
It's not something I'd loose any sleep over.
Here is the "fix" thread.....
https://ls1tech.com/forums/general-l...blems-fix.html
I heard the circuit boards crack and things on the board leak and if it doesn't work, your car stops working ( windows, radio, ignition, and ECU 
). Like I said, I know nothing about electrical stuff so all this might be a very easy fix, but it got me a little worried.
). Like I said, I know nothing about electrical stuff so all this might be a very easy fix, but it got me a little worried. Joined: Nov 2001
Posts: 34,631
Likes: 2,555
From: Schiller Park, ILL Member: #317
That's news to me. All I've heard about are some of the solder points developing hairline cracks. This can be fixed, and it's described in the link I posted.
Any part can fail, but the only "common" (and I use that word loosely, since many people have never had a problem at all) issue with the BCM are those solder cracks.
Any part can fail, but the only "common" (and I use that word loosely, since many people have never had a problem at all) issue with the BCM are those solder cracks.
That's news to me. All I've heard about are some of the solder points developing hairline cracks. This can be fixed, and it's described in the link I posted.
Any part can fail, but the only "common" (and I use that word loosely, since many people have never had a problem at all) issue with the BCM are those solder cracks.
Any part can fail, but the only "common" (and I use that word loosely, since many people have never had a problem at all) issue with the BCM are those solder cracks.
Joined: Aug 2007
Posts: 24,241
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From: Turnin' Wrenches Infractions: 005
Not a big deal at all. The BCM controls the body electronics, it does not control the engine, the ECM does that. The ECM needs the VATS disable signal from the BCM to start and run the car but VATS can be disabled in the ECM program so a working BCM is not needed for an engine to run properly.
Not a big deal at all. The BCM controls the body electronics, it does not control the engine, the ECM does that. The ECM needs the VATS disable signal from the BCM to start and run the car but VATS can be disabled in the ECM program so a working BCM is not needed for an engine to run properly.
Last edited by RONIN LSX; Jun 18, 2011 at 04:51 PM.
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There is a yellow/black wire that goes from the starter relay to the bcm. If you cut that wire and ground the end that goes into the relay it will bypass the bcm's control over it. I had to do this to mine when my vats quit working and left me stranded.
I need to do a complete run through of my dash wiring. Someone tried to steel the car from the previous owner and almost fucked up the column beyond use. I'll look into all this when I get to that point I guess. Thanks for the tip
well I did this, and confirmed that my starter works and it turns over now, but it still won't run on its own yet. I ran a jumper first to make sure. is there something else I need to gound in order to make this fully functional. I coukd careless if vats ever works again, I jusy want my car to run everything I stick the key on the ignition. I know my keys worn out and is part of the issue. its been giving me grief for years but its finally become its time and the old 98 key is no longer doing it. and I'm not willing to buy a new BCM nor a bunch of keys to see which one will work. already had VATS disabled in the tune but still got the P1626 code for VATS. so time to eliminate it.
Joined: Nov 2003
Posts: 6,216
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From: Wichita KS / Rancho San Diego
The way to solve your problem is to "bypass VATS" by putting a resistor with the same resistance as your key pellet inline that gives the proper signal to the BCM to energize the fuel pump. The BCM controls other things like power windows and sound system functions. Unless you're stripping the car out to be a full-on race car, it's not a good idea to bypass the BCM.
Joined: Nov 2003
Posts: 11,328
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From: Jacksonville, FL (originally from Toronto Canada)
RevGTO is correct... the proper way to eliminate VATS is to install the resistor bypass. VATS prevents vehicle theft when the correct key isn't found in two ways - it disables the ground to the starter relay to prevent starting and it disables the "fuel enable" signal to the PCM to prevent the engine from running due to lack of fuel. Grounding the yellow/black wire keeps the BCM from preventing cranking but does nothing about the fuel enable signal. You can program the PCM to ignore the missing fuel enable signal (what some programmers incorrectly call bypassing VATS) and you car will start and run although the SECURITY light in the cluster will be on all the time. I suppose a strip of electrical tape could resolve that issue. Bypassing VATS the correct way with resistors takes care of the starter relay, the fuel enable signal, AND the SECURITY light.
ok, im getting 13 through 15 resistors then, as my key ohm out at 8800. My voltmeter is kinda cheap so I'm covering my bases to see which one will work. 14 to 15 skips like al of 8000 range so i found it weird. I'll hook the yellow wire back up unless I can leave it ground directly to ground.
Joined: Nov 2003
Posts: 11,328
Likes: 346
From: Jacksonville, FL (originally from Toronto Canada)
I think you may have your meter on the wrong scale and actually have the #4 resistor value (887 ohms). There is nothing around 8800 although the next highest 9530 is within 10%.
You can get close to 887 using standard resistor values with 820 + 68 (888 total) or 620 + 270 (890 total) in series or with 1600 || 2000 in parallel (888.9 ohms net). None of the 15 GM standard VATS resistor values take more than two resistors to match.
You can get close to 887 using standard resistor values with 820 + 68 (888 total) or 620 + 270 (890 total) in series or with 1600 || 2000 in parallel (888.9 ohms net). None of the 15 GM standard VATS resistor values take more than two resistors to match.
Yeah im getting a better multimeter. Something digital. I had a cheapy one from walmart laying around, but hadnt needed a dedicated multimeter until now. I have a bunch of resistors coming i can test out within the range I need.
Joined: Nov 2003
Posts: 6,216
Likes: 236
From: Wichita KS / Rancho San Diego
You can program the PCM to ignore the missing fuel enable signal (what some programmers incorrectly call bypassing VATS) and you car will start and run although the SECURITY light in the cluster will be on all the time. I suppose a strip of electrical tape could resolve that issue. Bypassing VATS the correct way with resistors takes care of the starter relay, the fuel enable signal, AND the SECURITY light.
Joined: Nov 2003
Posts: 11,328
Likes: 346
From: Jacksonville, FL (originally from Toronto Canada)
VATS is designed to assume that if it discovers a problem with the key resistance while the car is running then it will assume there is a hardware fault rather than a theft and not prevent the car from starting. However, there have been reports of the system "discovering" the fault anew after a reset action such as a battery replacement and then preventing the car from starting. This does not happen consistently so I can't tell you whether it has to do with the amount of time the power is disconnected or some other factor. Obviously you will have replaced your battery within the last 12 years so it's not just replacing the battery which can cause this "reset". I mention it just so you will be cautious about the possibility should you have a need to leave the power disconnected for an extended period.