SO swapped out my PCM and all set running decent but keep getting the damn P101 code for TCM loss communication. Anyone have an ideas on this driving me up the wall. 07 Tahoe with ly6 swap

 

im assuming you are running an e38? is the e38 tcm (t42) flashed for the specific transmission you are running? do you have a 4l80 or 4l60? The tranny will act up if not flashed properly. If you have a 4l60 and you have a ly6 pcm then you need to get a 4l60 tcm and or flash the ly6 file for a 4l60.

 

Dont know how you programmed it but the easiest thing to do is leave the truck flashed for your OE vin to your truck using the PCM and TCM that are original to your vehicle.

Then overwrite the 6.0 values in the pcm using tuning software and the truck will function factory correct.

If it's done this way and you are still having trouble then there is a high speed data communication problem on the databus.

If it is not done this way and the pcm is using a LY6 based vin. Then LY6 vin programmed pcm is setting the above code because it is trying to communicate with a 6L90 TCM and is instead seeing a 4L70 TCM and the two use a different communication protocol and the code sets.

It works like this the pcm goes hey you out there on the high speed bus in english then the tcm then answers back in german and the PCM is expecting english and then goes WTF and then sets the u101 cause the 2 cannot communicate.