Yes batteries isolated all the time. Spent some time with my Delphi plugged in. I have come up with VIC codes:
27201-19 Engine running output, interruption or short circuit to ground. Permanent. The DAVIE manual shows "No CAN message received ’ Engine speed’.
24201-19 CAN message from ECU. Interruption or short circuit to ground. Permanent. Can’t find this in DAVIE manual
24205-19 CAN message from Tachograph. Interruption or short to ground. Intermittent.
Wondering from 1st code, if it is a crank sensor issue. Will remove and clean sensor and ring.