1999 v70 xc transmission, has a master mechanic and specialty shop stumped

[misha]

The shop has the specific Volvo scanning tool that can communicate with the TCM, they couldn’t find anything

What abscate asked!
Also...let them check ECU too for stored codes.
In rare cases TCM sends request to ECU to turn on CEL when specific codes are stored.

[wizechatmgr]

Anyone look at the ABS module? I thought you could also get this scenario if you have a bad PNP switch or the ABS module was ready to go kaput. This is of course assuming that I remember correctly, which may be a bad assumption.

On my '99 if the voltage isn't >=~12.5V it will eventually leave the car nothing but idling. The transmission will not engage. If I remember correctly both the transmission control module and the abs module can be scanned for their current B+ values.

[misha]

Abs module can't affect functionality of transmission....but since it's '99 and modules are married with the car....lack of communication between modules can affect anything because of CAN network.