A Time to Speak Italian
This past week I had the opportunity to get out of the cold and work on some exotic cars. We had a cold snap in Utah. I went down to Las Vegas. I had a customer purchase a scan tool from me and we used it along with some other tools to move a repair job forward that was not going anywhere. The customer complaint was that the vehicle would not crank or start. The technician had tried a new ecu and matched body control module to get it to crank but it was not happening. The tech thought the issue was with the immobilizer. He also told me that he could put power to the starter at the relay and it would start. That did not seem like immobilizer to me.
After connecting with the scan tool and attempting starts it was clear to me that the issue was not with the immobilizer. The immo lamp only stayed on for a second and then turned off. Fortunately the shop had wiring diagrams. We pulled one for the starter relay and could see that one of the primary wires went to the key switch / immobilizer and the other went to the transmission controller. There were no codes in the engine or transmission controller. We got out the circuit smoker (power probe) and connected to each of the primary wires. We set the tool to scream at us if there were ground or power. After turning the ignition switch there was a tone heard. So we know that the immo part of the circuit is good. No matter what we tried, there was no ground coming from the transmission. We decided to connect a ground and see if the vehicle would start.
With the ground the vehicle would start. Once started, there was no engagement of the F1 transmission. We thought maybe a disconnected wire between the paddle shifters and the transmission controller but we could see a change in state when each paddle was moved.
The customer had a spare TCM to try. Same result. No codes and no start. I had to hit the road but it felt good to get a vehicle further down the diagnostic path. The customer is convinced it is a bad TCM. It could be. Maybe the spare was one exchanged before. This was a vehicle that I was not familiar with. It proves to me when you have service information and the right tools you can work on about anything.
One note on the diagrams. Even though the printing was in English, the wire colors were not. Fortunately the key was there to tell you what the letters meant.
As always Mike, nice job. Thx for sharing this!
Bravo, this post is why I subscribe to forums like this. I would go with TCM as I learned wayyyy long ago an Automotive Logic Module is nothing more that a smart path to ground. I also learned that outside of environment (water, dust, static) what kills em is when too much current is flowing through the ground path provided by the module it turns from a ground to a short. If it is turning into…
Thanks for sharing.I'm glad you are in this forum.
What did you use for a scan tool on this thing?
Hi Rudy, I used the TEXA Supercar package that I sold to the customer. -Mike
Thanks for sharing... this video helps explain a lot for certain situations. youtube.com/watch?v=AtWc2i…
Hi Elias: Dmitriy is absolutely correct. I've had 8 or 9 GMs and a Caravan that erased the VIN. The only symptom with the GMs were that the SRS lamp was illuminated. The Caravan was a no start. All were recovered by programming the module (VIN programming using a DRB-III for the Caravan). BTW, I've had people tell me this is impossible. Guess that I should've bought some lottery…