No communication with DIM or DEM, BCM and REM intermittent

[tightmopedman9]

2003 XC70

Been trying to troubleshoot a problem on a friend's car. He bought it without a functional DIM, but otherwise the car seemed to function fine. Occasionally the DIM would kick back into life while driving. I re-flowed all the solder connections on the DIM and it started working for a few weeks more frequently than it had before. Now, only the check engine light will work on the DIM.

Yesterday we tried to determine why the AWD was not working. Using VIDA we found that the DIM and DEM were offline. The DEM is getting voltage at the module, and I tried a known good DEM module, which did not fix the problem.

We tried swapping in a known good used DIM of the same part number, which did not work. After trying the DIM swap the car was stuck in no CAN mode, with the transmission staying in 3rd gear. Pulling the battery cable did not remove it from the mode, but after clearing codes it started shifting.

Sometimes, after pulling the battery cable the BCM or REM will go offline.

I swapped in a new CEM by swapping the EEPROM chip containing the immobilizer code, and also changed all relays on the CEM. This did not resolve the problem either.

I'm looking for what other areas I can check, as right now I'm not sure what else to look at.