T43 Controller Not Detected

I have an LV3/6L80E combo that has been working reasonably well up until today, when it all of a sudden says it has a "Transmission Range Malfunction" when trying to access DVT controls for the E92 ECM. It has also had the effect of limiting throttle control, even though there are no DTC's referring to the TCM. I can flash to this TCM, but when I try to Scan, none of the PIDS will validate because it doesn't detect the controller. I've checked for 12v at the trans connector and that is good. Anyone have any quick troubleshooting advice for this? I'm supposed to leave for Drag Week on Saturday, and all was good up until this happened.

Hiya,
On the bench, I have had to put a 120ohm CAN "termination" resistor across the CAN line with efilive and hpt to get them to "talk".

This has been a working combo for the last couple of years, and then all of a sudden yesterday when I went to start a datalog, it gave me this issue.

Well it appears as though I found the issue, although the fix is a little surprising. Because of the original "Range Malfunction" message, I figured I'd look into the IMS (mode switch) to see if there might be an issue with it. I checked for continuity in the switch connector with the selector at various positions and found the readings inconsistent. I pulled the switch and opened it up to clean it. The stainless strips inside were a little dirty so I took a swab and some electrical parts cleaner to it and cleaned up the strips. To my surprise the readings were way better afterwards, so i reinstalled it and lo and behold, the scanner connected and read the mode switch. Everything looks good now, and i have my throttle back, since the lack of comms killed the ETC previously.

Hiya,
Thanks for the reply. I am not familiar with what a LV3 or this mode switch you are talking about. Can you point me to a link or describe it better for me? Thank You.
-Carl

Hi Carl,

LV3 is a 4.3L V6 from 2014- Silverado, and I'll attach a picture of the Internal Mode Switch, it is attached to the shift selector detent and tells the TCM what position the shifter is in.
Attachment 24484

Okay officially panicking now. Apparently that didn't fix it, because I went for a drive today and all was good, until I did a Cal Flash for a little change in shift speed and it happened again. It gave me a Checksum Invalid and again I have no throttle and the T43 TCM can't be detected again. I'm supposed to load up for Drag Week tomorrow, and it's starting to feel like I may have to cancel again if this doesn't get sorted. Any other ideas?

It's a little late to update this, but the problem was with the fact that I still had an Edge dash hooked to the Canbus when I made these changes. I realized after that having another item on the bus is not a good idea when flashing or reading, all is good now and Drag Week was successful.

Thanks for the reply, glad to hear you had a good week :)

Goid thing you found the cause :cheers: