Body control module (BCM) replacement

Tiny
IRENECURLIS
  • MEMBER
  • 2005 CHEVROLET MALIBU
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 41,000 MILES
How do you replace BCM in car listed above that is the Maxx model?
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Thursday, March 10th, 2011 AT 7:39 PM

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Tiny
RASMATAZ
  • MEMBER
The BCM in your vehicle is tied to the other computers/modules and must be programmed. I do not recommend trying to just plug in another one as it will cause other issues.

See diagram below for programming procedure before beginning.
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Thursday, March 10th, 2011 AT 7:43 PM
Tiny
CARADIODOC
  • EXPERT
Hold on! Let the dealer take on the responsibility! All of the other computers on the car are tied to the body computer which has the vehicle ID number programmed in. If the new computer is not programmed properly the first time, all of the other computers will have to be replaced and programmed by the dealer. It is that type of business practice that makes GM so profitable. It is also possible that someone in the past pressed the "lock" function on the GM scanner. You would not notice anything with the operation of the car, until you have to replace the body computer. There is no way to undo that lock procedure. It electronically locks every computer module on the car to that body computer. It makes every one of them worthless as far as installing them on a different car because they can not be reprogrammed. (How does that benefit the customer)? If that lock button was pressed, you will have to replace every computer on the car along with the body computer. (There can be up to forty seven computers at last count). Also, most body computers are built into the radios now on GM vehicles since 2002 models. That is to prevent you from buying an aftermarket replacement radio. You are tied to the dealer and their very expensive repair centers. There is a reason GM was having trouble selling to repeat customers.
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Thursday, March 10th, 2011 AT 8:05 PM
Tiny
BMONTY40
  • MEMBER
@CARADIODOC. That is completely not true. Just this weekend I picked up a used BCM from the local pull-a-part. I tried it in my 2005 Chevrolet Classic and it made everything come back to life except the engine would not start. That night I was looking for a place to get a re manufactured or a new one, and then have it reprogrammed, when my son suggested we go back and get the PCM from the same car. I thought about it and could not find a reason not to, so we put it in the car and turned the key and it started up just fine. Turned out the only two that had to match up was the BCM and the PCM, oh yea, and the radio. The radio is showing LOC, so we are going back today and get the radio from the same car. I am thinking it is going to work also.

So if you want to use one from a junk yard just make sure to get both of them. Along with the radio.
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Monday, September 17th, 2018 AT 7:05 AM
Tiny
CARADIODOC
  • EXPERT
What I did was to offer a less-than-ideal explanation of what could happen. That has to do with the "Lock" procedure. That obviously was not done on your car by a disgruntled mechanic. There is no reason that option should even be designed in by the engineers as it is only useful to GM so more of their cars will cost too much to repair, so you will buy a new one.

My reason for sending the customer to the dealership is to avoid exactly what you went through. You are replacing multiple modules to solve a problem and to get all the features and options working again. Let the dealer have to confront the customer and explain why they need to buy so many seemingly unneeded parts. GM started this on only a few 2002 truck models. It did not show up on other models for a number of years later. If the radio's display shows, "Lock", that is not related to the computers you replaced. It is quite possible this design trick does not apply to your car. That would make me happy. If you get a different radio, it is just as likely that one will also be locked by the previous owner. If this is the same as those in older models, all you have to do is type in the code number to unlock it. If you do not know that number, the dealer can tell you how to enter a few button presses to get a number on the display, then the people at the dealer's parts department can call an "800" number to translate it to get the unlock code. Of course they do not do that for free, but at least you do not have to buy a different radio.

This post is over seven years old, and I have learned a lot since then. I have run into other people who also did not experience what I warned about, but I have also read about at least two instances where my warning was right. Imagine how I would feel if someone reported back that they had to replace dozens of computers and I did not at least mention my warning.

As a side note, I have been to sixteen of the Pull-A-Part yards. The employees and the customers at every one was very friendly and helpful. Parts are inexpensive and the yards are all very clean and well-organized.
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Monday, September 17th, 2018 AT 12:37 PM
Tiny
BMONTY40
  • MEMBER
What I did was, save my son a ton of money, by not having his car towed to the dealer and then the five or six hundred dollars to have the BCM replaced and programmed. It was only $56.00 for the two computers.

The radio worked until I switched the BCM so when I get the radio from the donor car, I am sure it will work without the lock showing on its display.

The BCM is programed to the PCM (computer), and the car will not run if you try to pair a different one up with the computer, but all those other ones you talk had no effect. Once I got the computer from the car I got the BCM from, it ran.

I truly did not expect this to happen, I thought as you do, there were other things that were tied to the computer but I am glad to say I was wrong. Well, other than the radio.

I posted this to let others know there is another way of replacing their BCM without having to go to the dealer and pay those high prices and pay for a tow.
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Monday, September 17th, 2018 AT 1:04 PM
Tiny
CARADIODOC
  • EXPERT
One more thing I thought of later was my entire reply does not apply to your car. That is because you have a separate Body Computer and radio. GM has pulled a number of tricks to stop me from repairing their radios for dealers around my state. One was to no longer allow me to buy their radio service manuals after the 1994 model year. Next, they had a one hundred percent failure rate on their laser assemblies on their CD players all through the 1990's, and with no service manuals, I could not get part numbers, so I could not order parts. To avoid the high cost of going through the dealer to one of their two remaining authorized repair centers, most people just went to Best Buy to get a decent aftermarket radio. This is where my story begins. To combat that, GM started building their Body Computers into their radios on some 2002 truck models so you could not remove their radio. If you did, you would lose the turn signal click, power locks, interior lights, and other systems. When you needed a new Body Computer, you were actually buying a new radio, and the dealer had to [program it to your vehicle. This did not extend to all the other truck and car models for possibly another eight to ten years.

The aftermarket industry fought back again by offering a "radio relocation kit". That was a long wiring harness that allowed you to mount the original radio under the passenger seat, and just cut off the speaker wires and run them to your new aftermarket radio in the dash. That way you still had the required Body Computer/radio connected and working.

Chrysler also had some similar issues with matched Body and Engine Computers, but the problem was a little different. It is worth mentioning in case someone researching this topic reads this. Some early 1990's models were available with or without the factory anti-theft system. That was built into both of those computers. When you installed a used computer into your car with the anti-theft system, if the used computer did not have that programming, it would learn it from the other computer the next time the ignition switch was turned on. Basically, you could use any computer if your car had the anti-theft system.

It is when your car does not have the anti-theft system that it gets messy. If you install a used computer that also does not have it, it will work just fine, but if you get your hands on a computer that was in a donor car that had anti-theft, that is burned in permanently and cannot be undone. When you turn on the ignition switch, the used computer will teach the other one that it should be upgraded to anti-theft status, so now both of those computers will only work in any similar model that has the anti-theft in it. Since your car does not have anti-theft, both computers are now self-taught to wait to see the disarm signal before they will let the engine start and run, but there is nothing on the car to generate that signal. You can pull your hair out swapping computers in and out until you finally hit on two at the same time that do not have the anti-theft programming. Since you typically do not know the history of the donor cars in the salvage yards, the safer way is to buy a rebuilt computer from the dealer. They all come with no anti-theft programming, then the new one will learn it from the other computer if that option is on that car.

Regardless, please pop back with an update when the radio is working. Thank you for adding to this post as it is likely to help others.
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Monday, September 17th, 2018 AT 9:51 PM
Tiny
BMONTY40
  • MEMBER
Okay, I have an update: We got the radio from the same car, plugged it in, and it worked! It was already paired up with the BCM, and the PCM, so it was like old friends getting back together.

And one more thing, yes my son's car does have the anti theft system in it, so all that stuff you were saying did not quite ring up as being right. Nice try though. I am not sure if the new stuff has the anti theft system or not.
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Wednesday, September 19th, 2018 AT 11:39 AM
Tiny
CARADIODOC
  • EXPERT
Dandy. Happy to hear everything is working again.
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Wednesday, September 19th, 2018 AT 2:58 PM

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