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Best way to remove Body Control Module (BCM)


sagrilarus
08-09-2007, 08:45 PM
I have a bad BCM and will replace it soon. I have opened up the bottom of the dash on the passenger side and can see it, and can reach it, but I can't figure a good way to remove it. I had expected a couple of screws attaching it to the body, but it seems to move around a bit, leading me to believe that it is fastened with Some of GM's plastic clip thingers.

If any of you have actually extracted one of these things and can give me some tips based on your hard-earned expertise, I would greatly appreciate it.

I have the following tools prepped and ready just in case:

1. Screwdriver
2. Wrench
3. Axe

Sag.

GregA
08-10-2007, 08:55 PM
I have the following tools prepped and ready just in case:

1. Screwdriver
2. Wrench
3. Axe

Hi Sag,

I like your choice of tools, especially the last one.

If I remember correctly, there is a plastic retainer that you have to push on, but otherwise the BCM just slides UP to come off of its mounting.

I have a could of pictures here (http://www.my-chevy-venture.com/Upgrade-Body-Control-Module-BCM.html), of when I upgraded mine.

Good Luck & Take Care,

dj1111
08-16-2007, 08:46 PM
What leads you to believe your BCM is bad. I thought mine was because the interior lights stopped going on. Everything else that it controlled worked fine. So I assumed it was the BCM. Turns out it was a broken wire under the passenger side carpet.

sagrilarus
08-17-2007, 09:47 PM
What leads you to believe your BCM is bad. I thought mine was because the interior lights stopped going on. Everything else that it controlled worked fine. So I assumed it was the BCM. Turns out it was a broken wire under the passenger side carpet.

A good question. The circuit that it is on began popping its fuse. At first just now and then, but after a while it became a daily thing. Fuses were cheap, so I replaced (I'm not much of a mechanic). Then the remote keyless entry and all the interior lights failed and have never returned (power locks and windows still function). And, the fuse stopped blowing.

My first thought was that the power surges blowing the fuse had damaged the BCM, but then when the car stopped burning up the fuses I considered that maybe the BCM itself was the heart of the problem, or perhaps the plug leading into it. My plan was to get under there and get the plug loose and check the power on it, and then switch out the BCM with a replacement.

Naturally I am all ears on other ideas for figuring this critter out. If it's wiring under the seat, where would you recommend I look, and what should I look for? A beer will be mailed to the car geek who leads me to my problem.

Sag.

dj1111
08-18-2007, 02:54 PM
There's a lot of wires coming out of the BCM going in many directions. My bad wire was under the carpet on the passenger side. Pull off the triangular kick panel (trim) at the passengers feet just below where the BCM resides. Then pull up the trim, I guess you'd call it the threshold below the passenger door. After that you can pull back the carpet to expose the wires underneath. It seems those wires, especially towards the front of that area, are prone to getting and staying wet and sooner or later breakdown, corrode then break or short or both. To find my broken wire I peeled off all the black tape to expose the entire length of that wire cluster. Didn't take long to find the bad one. Many of the wires were very stained with rust. Good luck. If you try this make sure you tape the wires back up good with high quality electrical tape.

sagrilarus
08-18-2007, 06:41 PM
Alright, so here's where it stands. I cracked open that side column and the edging on the door frame, lifted the carpet and sure enough there was water. Not just a bit -- the entire harness was lying in a pool of water. But on inspection, the wires did not seem damaged, and there was no discoloration or rust. The tape wrapping them was about useless though.

So I kept moving the bundle with the key in the ignition and the driver door open, hoping that I would jiggle a ring out of the open door alarm -- no luck. The wires all seemed intact and in good operating order.

So I thought it through a bit more. EVERYTHING from that BCM was out, and I had the underside half open so I reached up in and tried to futz the BCM out of its holder. It dropped into my hand and I have no idea what I did. But, there it was, so I set the axe aside and got to work on it.

Step one was to see if it was getting power. Damn near had to pick up the axe again to get the power coupling out of the unit. Finally managed to get it loose and found power on the plug. Good news. Next step was to check the outputs.

I plugged the power plug back into the BCM, then damn near whacked my head on the underside of the glove-box when it started pinging the open-door alarm! BCMs are remarkably loud when you're six inches away from them. Remote Keyless was functioning properly, lights, alarms, the works.

The leads for the plug looked very clean when it was apart, and with it working I quickly declared victory and put everything back. My finely-tuned mechanic skills had fixed this challenging problem.

No clue why it failed or why it started working again, and I get the feeling that I'll be back under that dash. But for the moment I'm back in the game.

Please forward me your addresses so that I can send beer. Much obliged for the help.

Sag.

dj1111
08-18-2007, 09:14 PM
Doesn't it feel great to have lights again? I lived with it for many months fearing what it would cost to fix. When in the end it cost next to nothing. It still troubles me that you were blowing fuses left and right. There had to be an overload somewhere. A shorted wire perhaps that you jiggled out of its shorted condition when moving things around?

Your thanks is all I need, not a drinker. See ya around the forum.

bigcoconut
08-19-2007, 12:45 PM
I had a similar problem with my door locks and tracked it to the wires under the carpet. I had to replace/fix three connections under there. Have you figure out how the water got there in the first place?

My advice on that one, if you need it, is to look for the drain pipe outside the firewall for the AC evaporator in the dash. The drain is a royal pain ITA to locate, you may have to "feel" for it between the motor and firewall. There should be an elbow connection and a drain hose all the way down to or below the frame. If there isn't one than the water that is exiting the AC evaporator is getting blown back against and through the firewall then soaking into the carpet. I can pretty much gaurantee that if this is the problem the carpet will be soaked again, the next day.

dj1111
08-20-2007, 07:39 PM
I think most of the water under my carpeting comes in the winter from all the snow, ice and salty slush you bring in with your shoes. That's probably the reason I found a lot of rust stains, the stupid salt. When I fixed it recently it was dry. I also found evidence of other wire repairs in the same location.

bigcoconut
08-20-2007, 09:25 PM
Down here in Houston, we don't concern ourselves too much with the snow and salty roads in the winter, just the hurricane driven rain and small trees/buildings that occasionaly find there way airborn. And with the hot sticky summer's you run the AC constantly, and therefore under your car looks like a lake when you're standing still.

Sounds like you got it figured, see you around the forums.

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