A Case of Mistaken Identity Part 1

Here is one 2001 Saturn L100 vehicle with 111,901 miles on it. The vehicle has been in a collision event and has had a host of "donor" parts installed. The car supposedly ran no problem before being shipped off to the body shop. The trouble at hand now is a start and stall situation. The funny thing is if the battery is disconnected and reconnected the vehicle will start and stay running. Just don't turn it off it will revert back to the start and stall situation. Various people have looked at the vehicle. It was determined that the BCM (Body Control Module) was bad. That is a fair assumption on this vehicle. I do a ton of BCM replacement/programming on Saturn vehicles. A used BCM was installed and still had the same issue. Well, this is where I tell the shop a used Saturn BCM is a definite no no. Saturn BCM's are VIN locked once programmed to a car they cannot be successfully reprogrammed to another vehicle. Yes, you can use them but you will issues such as airbags inoperative due to the VIN mismatch, accessories not working properly, and my favorite mileage change. I do a quick visual on the car and then check for codes.

I pull a U2105 and a U2106 out of the BCM. These are CAN (Controller Area Network) codes concerning module to module communications. Here are the codes and code set criteria.

Something is not sitting well with me at this point. Saturn is like the bastard child of GM. Take what you know about GM and throw it out when dealing with the Saturn platform. It keeps you on your toes for sure. I am looking at these codes and the code set criteria. Something is gnawing at me. I decide to look at some wiring.

I combined both the Saturn L100 2.2 Liter L61 wiring and the 2001 Saturn L300 3.0 Liter L81 wiring together. A couple of observations the L300 L81 utilizes a CAN network and a separate TCM (Transmission Control Module). The L100 L61 platform is pure Class 2 with no separate TCM. I had my first clue. I ask the shop for the replacement used BCM that he used.

No doubt this is a used unit. Junkyard writing galore. It finally hits me. I pop the original BCM out of the car to look at that.

Well they got the same one they had that is for sure. Hmmm it hits me....

They have V6 BCM's!!!!!!!! That is the reason for the CAN codes and the start and stall issue. I inform the shop who tells me how did this happen? I wish I knew. I tell him he needs a new BCM and I will program it for him. The next question is...... wait for it "Why can't I go with a used unit?" "I am losing my shirt on this car" "There is got be another reason"
After informing the shop I will have no part of a used unit he reluctantly agrees.

  
The new BCM arrives. Notice something different? I install and program the BCM. Relearn the theft deterrent and it start and stays running. Now he can concentrate on the other issues with this vehicle.