DTC codes D900 and E510 are exactly the same as U1900 and U2510.
Some of the can-bus seams to be working still. Otherwise the AA couldn't have read the 2 U codes.

So, it's probably not an ecu hanging up the bus, but a wiring problem in the can-bus somewhere between the instrument panel and the engine ecu and transmission ecu.
It's not between the instrument panel and the diagnostic connector. It is however also between the diagnostic connector and the engine and transmission ecu's.