Volvo Repair: XC70 all electronics shut off - engine is running but stuck at 4th gear, srs airbag, airbag service

Question
I have 2004 XC70. Two weeks ago, while driving on a hwy at about 120 km/hr, the gear all of the sudden shifted by itself from the 5th gear to 4th gear. Since it was in the automatic mode, the car immediately shifted back up again to 5th gear, but then a few seconds later it again shifted down to 4th gear. After a few times of this the message "Brake Failure Stop Safely" came on. A few seconds later all the electronics died, the odometer, RPM, gas and temp gauge...everything shut off (just like when you turned off the engine). But the car engine was still on and I could keep driving, but the gear stuck at the 4th gear even when I stopped. Even the manual shifting geartronic did not work. I stopped the car, turned off the engine, waited a few seconds then restarted it, and "SRS Airbag Service Urgent" message came on. I drove the car again, and about 30 minutes later, it started doing exactly the same thing. So I stopped the car, get it towed to the nearest dealer and left the car there. The dealer checked everything and could not find anything wrong. But in their invoice they wrote the following:
DTC Codes: 928C, 530B, 4050.
SRS: 00D5 perform diag as per VIDA.
All DTC codes related to CAN data communication.

I would much appreciate if you could tell me what all these mean. I'm afraid that the real problem has not been addressed. I'm afraid it could be transmission, or at least the on-board computer that controls the automatic shifting. Thanks in advance for your time.

Answer
All of those codes pertain to control module communication along the CAN network (the computer network used for all the cars modules to communicate with each other).  They all share information with each other and when communication is interuppted and some modules lose portions of the data they need to run, a whole lot of weird symptoms will start occuring (like you have been having).  The problem is going to be isolated to a bad module clogging up the network with bad signals, or a wiring issue for the network wires interrupting communication.  Can't really say which it is but I know it will be difficult to find.  They may need your car for a period of days maybe more than a week or 2 to get anything from it.

James