P2 2001 V70 T5 Sudden Massive Electrical Failure

Brickbat · Post by **Brickbat** » 30 Oct 2017, 10:23

Hi all, I’m fighting a weird problem. I’ve owned the car for 5 years – at 195 k miles, it’s well maintained, and prior to a few days ago, there had been no hints of this electrical issue.
I had just exited the highway 3 days ago, and while coasting down the exit ramp, the instrument cluster went totally dead. The engine stopped. No lights, no radio, no power windows, no central locking, no idiot lights, no heater, NO EMERGENCY FLASHERS. Nothing, except oddly, the engine still cranks fine, so I don’t see how it’d be a battery failure.
I had to have the car towed home.

When I turned on the ignition, nothing get energized except a little relay clicks somewhere on the passenger side of the dash.

I've found two clusters of 'main' fuses (in the cargo area near the battery and the ‘lower layer’ in the engine fuse box (60A and 50A) and they all looked good. After poking around in all the fuse boxes and finding no open fuses, I reconnected the battery ground. (I had it disconnected since getting to the underside of the under-hood fuse box requires that).

When I reconnected the battery ground, the car interior lights came on! Everything was dead before -so that was unexpected.

I tried to start the car, and it started up and the engine ran normally. There was now a SRS airbag fault, presumably because I didn't have the ignition switch in position 2 when I reconnected the battery. But otherwise all seemed good. For a while...

I took a short drive, and the car died again. As it was dying, the first hint was a BRAKING SYSTEM fault popping up, the instrument cluster froze. I continued to drive and a minute later the engine stalled. As with the first time, the starter was able to turn the engine over normally, but the engine wouldn't start, and all electrical devices I could think of testing were dead.

I disconnected the battery ground for a minute, and when I reconnected it I had the same result - the interior lights came on, and I was able to restart the car. I drove it home, and it's sitting here, idling away fine for the last hour.
It appears to me as if the electrical system loses connection to the battery, or at least most of the system, with the exception of the starter does. Then the car continues to run on alternator power until the engine rpm’s drop so low the alternator can’t keep up, and the car stalls.
I’m carefully going through all the main fuse box connections, and all look great so far (i.e. nothing seems loose, burned, or corroded)

RECAPPING – Car loses all electrical power while driving. Nothing electrical works except the starter, which cranks the engine fine, but the engine won’t restart until some time after the battery ground is disconnected and reconnected.

MAIN QUESTION: Are these symptoms at all consistent with a CEM, REM, or other module failure?, or should I keep looking for intermittent power wiring issues?

Thanks,

Jim
(noob here, but been driving and maintaining my own Volvos for >20 yrs...)

Post by **abscate** » 30 Oct 2017, 11:27

Welcome to MVS Jim!

Electrical troubleshooting is a process where you start at an electrical part that doesn't work - and start working back to find where voltage to the part has been interrupted.

Here you can choose from many parts to find the fault!!

The common thing here, and a known high-mileage-failure part, is the electrical part of the ignition switch. There are a couple of threads here on this - I think the 2001 is the first P2 style switch.

Post by **abscate** » 30 Oct 2017, 14:13

Elaborating a bit more. Most everything electrical in these cars gets powered through a relay which is triggered by the ignition switch for either function or load reduction. When the contacts in the ignition switch get worn or dirty it takes out the relays which wipe out electrical function.

Jiggling the key is a imperfect diagnostic, if it helps it points to the switch but if it doesn't , it's not too indicative. The electrical part is separated from the key tumbler.

Post by **precopster** » 30 Oct 2017, 14:14

The most important thing when fault finding is to use a test lamp connected to the fuses rather than a visual check. Also a volt meter offers no load to the circuit so avoid this and ONLY use a test light.

Once you work out which circuits are dead you can work through the electrical diagrams to isolate which 12V feeds are suspect.

Brickbat · Post by **Brickbat** » 30 Oct 2017, 14:54

Yeah - So I had been thinking about the ignition switch. I never would have guessed that a failed ignition switch would result in all electrical devices (including the hazard flashers) going down.

That, plus the fact that both times the car died in this manner, a disconnect-reconnect sequence of the battery restored to to life.

At this point, I need it to die again, but I'm not too anxious to take it for a ride. (I mean, I like my tow truck driver and all, but...)

Post by **JRL** » 30 Oct 2017, 14:57

Wiggle the key while it's running (and parked AND at your home)!
and see what, if anything, happens.

Brickbat · Post by **Brickbat** » 30 Oct 2017, 15:00

^^ sure - easy enough, and I'll definitely try that. I've already went around tapping on all three fuseboxes while it was idling, and didn't see anything interesting.

Post by **mrbrian200** » 30 Oct 2017, 16:34

If it turns out not to be the ignition switch, the second thing I would look at would be the smaller red wire that goes to the small fuse box next to the battery. The systems going dead (yet the starter cranks) might be consistent with this circuit being open between the battery and that little fuse box. Systems that get power through these circuits are the REM,CEM, most of the interior electronics, Low beams and puddle lamps. The ECU, TCM, and starter motor get main power through the large main (+) wire that feeds up to the engine compartment. But if the CEM isn't getting power it won't start because CANBUS goes down with the CEM.

Post by **oragex** » 30 Oct 2017, 17:11

Because of the hazard lights not working, I would also give the alternator (and its associated cables) a check. With the engine running, turn on as many electricals (high beams, radio, a/c, etc) and measure the voltage, then measure the battery.

Brickbat · Post by **Brickbat** » 30 Oct 2017, 20:04

First off, thanks for taking the time to read the story, and post up your ideas. I did try some vigorous key wiggling, and nothing happened, i.e the engine didn't stall, and all the accessories stayed running. The alternator is doing its job fine, keeping Vbat at 14-ish even at idle and with lots of accessories running.

I pulled out the battery, and carefully cleaned all the cable and fuse connections on the rear fuse holders, as suggested by mrbrian. Didn't see anything suspicious there. I'm going to pull the REM, and give it a careful visual inspection next as soon as I figure out how to remove the left side interior panel that's partially obstructing it...

Thanks again for the welcome and advice...