This is a follow up to the problem I posted. (Like many others out there). Guess what.... there is NO RECALL on the Memory Control Module Computer for the seat heater controls. Sorry, no freebies on this one. There is a TSB (Technical Service Bulletin) from GM that advises the repair shop (dealer) to investigate and install a new MCM (Mem Control Mod. So, sorry, there's no fix except to replace.....at your cost. But, I have good news! The GMC dealer only wants to charge us $495.00 for a new MCM! Isn't that great news! Uh.....no, it's not. I did, however, find that Ebay carries a stock of them (and a particular vendor that only stocks GM products). Ebay inputs them as "door switches", so be sure to look for your year and model with "door switch" as your search term. The vendor that supplies them on Ebay, and at their store front, is called "G and R Auto Parts" from Oklahoma City, OK. They only deal with GM used parts, and I found mine for $50! What a deal! I just installed mine and it works great! I called down to talk with them and they are great to deal with. Read on if you want to see the technical side of the repair.....
I consider myself a "weekend warrior" with computers and light mechanic work on cars, so I did my own diagnostics on the car to find the specific issue that caused the seat heaters to freak out. There are 2 computers that control the seats. One is located under the drivers seat in a black box about the size of a 5x7 picture frame (1 inch thick). The other computer is located under the window switches on the drivers door. Actually, the switches and computer are all one unit. The computer boards in this "switch box" control multiple things that I'm not entirely sure about. I do know this..... The green plug goes to the switch box for the seat memory/seat heater/ pedal memory. That's as far as we needed to go. With the standard varation control that we all learned in chemistry class to add/subtract one variable at a time, we deduced a couple of things. 1, the computer circuit board was reaching in excess of 330F degrees! We got the temp reading from an infrared thermometer for $15 at Radio Shack.(Good purchase!) I don't know much, but that can't be right. After we played around with that for a minute, we were able to tell that a certain computer chip was getting too much juice and it created jumps and skips in the controls that made the seat heater come on and off. It also got so hot that it initiated the windows and mirrors to do crazy things. Wild stuff! Then, we looked closer at the circuit boards..... there were a few burn marks by some resistors that just happened to be hooked up to the Green plug. Ahhhhh, the plot thickens. After that, we investigated a few more areas on the board and found that there was also a little corrosion around the green plug. Bingo! We theorized this..... Because the com chip got so hot (We don't know why, it's only got 81,xxx miles), the chip send a power surge to the green plug resistors. It burned out the resistors, thereby creating a dam for the power to go nowhere except burn the chip faster.(330F+) This initiates a powersurge in other areas and created the voodoo ghost effect of the seat heaters going on and off (And later the windows and mirrors). Because the chip burned the resistors, it burned off the protective coating that is applied to keep moisture out of the circuits and solder. This created the corrosion and possibly even more problems, but hey, it only took one time to see the effect. Crazy huh?!?!?!
There it is..... My theory and my fix. Hope this helps. As always, please contact me anytime if you have any problems.
Thanks and good luck.
Brandon
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