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Mr Diagnostic

The Mobile Automotive Diagnostics and Programming Leader in New England!

Beware of Used Parts

I have programmed used computers into vehicles for years now. Some times they work sometimes they don't, but I have never run into this!

   I was called in to a shop for a Malibu Max with a 3.5 engine. The complaint was the car was bought at auction and when they got it back to the shop the one and only computer ground wire was melted and when they unplugged the plug from the PCM the ground pin from the PCM was melted into the plug and came out with it. The customer bought a new plug and attached a new ground to it as well as moved every wire from the old plug to the new one. He then bought a used computer and plugged everything in. He still could not communicate with the known good USED PCM. Thats when he called me in. I checked all the powers and ground to the PCM and they were ok. I then checked the data lines from the diagnostic connector to the PCM and found this model runs on GMLAN only. There is no serial bus line direct to the PCM. I then chased the GMLAN lines and they were ok as well. This told me the known good USED PCM was still the problem. I then pinned out the connector the customer re- wired and every wire checked ok. I did more research and found if you use a PCM set up for the serial bus it would not communicate. I checked the part number of the used PCM and it was a serial PCM. I advised the customer to buy a new one from the dealer. We installed it and what do ya know... We had communication. I programmed it and it ran like a champ.

  Moral of the story... He would have saved time and money buying the new PCM in the first place!! Sometimes the cheap way out costs more in the long run!