P2 2001 V70 T5 Sudden Massive Electrical Failure

[Brickbat]

So, I finished looking over the REM (that's the fusebox/module on the drivers side of the cargo area). All looked good. I tested all the fuses, and re-seated all the relays. Not sure what to do next - the car is running fine here in the driveway - I guess I'll just go for a drive this weekend, tow truck driver phone number in-hand...

[abscate]

Pull the electrical part of the ignition switch and open it to have a look

Diagnosing CANBUS failures without VIDA is pretty much fruitless, so start thinking about finding someone with that

[Brickbat]

I'll look in to replacing the electrical part of the ignition switch. I did search here, and didn't see P2-related issues in that, but I'll dig some more.

CAN - yeah - that's scary, because right now, there's nothing to diagnose. There's a indy near me that has VIDA, (or at least enough of it to reset me airbag indicator), but I'd be curious what their first step would be...

The car ran fine during my weekend drives, but I still don't trust it...

[precopster]

In my earlier post I explained how to fault find using a test light. Vida will only show non communicating modules at the time of failure with no linking of how they're connected. Time to use wiring diagrams and test light.

[Brickbat]

Well, no point is that until the car fails again. I have a test light in the car, ready for that occurrence.

Question - If, say the CAN bus went down, is that likely to cause the massive failure that I described in post #1 (i.e every electrically-operated doo-dad in the car was dead except the starter.)

[precopster]

Usually no. Canbus is a protocol not a physical item you can touch. There are many test points to use.

This year I repaired an XC90 2007 with suspected Canbus issue. Door locks, climate control and another circuit I can't remember were down however were down permanently unlike yours.

It ended up being a corroded main power cable where it meets a connector in the left lower corner near the REM. There were just a few strands of copper still carrying voltage to the above modules. Testing with a meter showed voltage at all fuses however using a load (21W test lamp) showed otherwise.

[Brickbat]

...It ended up being a corroded main power cable where it meets a connector in the left lower corner near the REM...

Right - I was hoping to see some evidence of something like that in the REM or engine bay fuse panel. But, I've gone through both and despite being 16 years old, everything looks great. What happened to yours? Spend some time under water? Battery outgassing?

[abscate]

Cables corrode inside where you can't see. An IR viewer will reveal the heat from excess resistance though, as will touch.

[Brickbat]

Usually no. Canbus is a protocol not a physical item you can touch.

It's both, no? My review of the wiring diagram shows a differential-pair for all CAN signalling, that connects all nodes. See, e.g. P 40 - 42 of TP3977201, which shows the CAN wiring between the major modules. The LIN and MOST networks look similar, though appear to be single-ended, rather than differential.

Anyway, I don't understand what you mean when you say you can't 'touch' the canbus - it seems to me like just a wired, serial data bus...

[precopster]

Each node has 2 wires with a predetermined resistance either 64ohms or 128 ohms.

For example CEM, ECM, TCM and all others run run a data bus for programming. You may find Canbus activity with an oscilloscope but it is not present without power which is more likely your issue.
So searching for Canbus while fault occurs is pointless because it will be down.