2001 V70 electrical issues, CEM?

[hiroku]

My 2001 V70 developed some electrical issues, as if it's possessed by a demon.



It drove 100% fine, then I parked it for 30 minutes.

When turning on the ignition again, at first I got a "start not possible, please try again" message. Cranking was of course not possible.

Then red SRS and brake failure warnings started flashing on an off.

The instrument cluster was flickering, and I could hear the relays under the steering column clicking intermittently.

No power windows, no central locking.



I did a battery reset. Then only the SRS warning remained, so the engine could be started.

The engine ran fine, but several systems started to fail one after the other.

The headlights and taillghts were on, despite the switch being in the off position. Then they started flickering.

RPM gauge sometimes dropped to zero. The instrument cluster then failed completely except for the check engine light, then came back to life again.

At one point all front interior lights went off.

The only things that still seemed to work were the engine itself, the climate control, headlights, and the light in the trunk.

After another battery reset, it no longer started at all.



I checked whatever basics I could with the tools at my disposal at the time:

The battery is a 6-month old VARTA 105 Ah unit, fully charged. 12.6 V measured while parked, 13.9 V when the engine was running.

Breakdown/recovery hooked up the booster, no change.

Measured continuity on all fuses in the engine bay, all fine. Come to think of it, I should measure the ones on the passenger compartment as well...

All engine bay ground points look fine.

I could not read any fault codes as the OBD didn't have power. I'll try it later if the ignition switches on.

I did pressure wash the car the day before, and noticed the water pooled in the windshield cowling and did not drain as fast as it used to. Nevertheless, the carpets feel dry.



QUESTIONS:

- Can I assume this is the CEM?

- Should I look for any other causes, like any ground points or connectors inside the car, etc.



Advice appreciated, many thanks.

Victor

[jonesg]

I would read the codes first, erase them and see what comes back.
Make sure you get airflow to the ECM box.

[hiroku]

Codes cannot be read as the OBD has no comms.

I removed the CEM, inspected it thoroughly but no sign of water ingress whatsoever.
Cleaned it with contact spray, dried it with a blow drier and retested, no luck.

Checked and measured the ground point under the door sill plastic trim, all perfect.

All interior fuses checked OK.

On the relay holder in the CEM, I noticed that only CMI22 felt warm to the touch. Per the wiring diagram, it seems to be X feed (ignition position 1?) to the CCM and DIM (I have no power seats). The CCM did turn itself on while the key was nowhere near the car.

I'm aware these CEMs also suffer from overheating issues, but the symptoms are usually more intermittent. In my case the systems did start to fail one by one but within the space of one hour pretty much everything except for the horn and headlights seems to be completely dead.

Can I assume an internal failure of the CEM itself? Seems a fair bet that I need to replace the module, but I would like to rule out any underlying issues that could cause it to happen again.

[packetfire]

Assuming you can get it to talk to the ODBII port, it may simply be overheating. If you can't get it to talk, it may be in need of replacement.

Many V70s have overheating CEM chips. My solution was to add heat sinks to the CEM and REM chips. This is not hard to do at all, as the heat sinks are cheap, and one can by thermal double-sided tape to attach them.

Here is a post with the heatsink size for the "main" chip (1-inch square), but I put a heatsink on all the larger chips, as I had a junk box full of various sizes sitting unused.

https://www.volvoxc.com/forums/showthre ... 04-CEM-CPU

There are all kinds of wacky approaches, one fellow got a 12-volt fan and installed in permanently under the dash,

[hiroku]

No comms whatsoever. The car has been completely dead since I posted this, even when stone cold.

Is the overheating known to cause permanent damage? The failure I experienced was very sudden - the car went from being 100% fine one minute, to all systems failing one by one, to nothing working at all within the space of about one hour. Certainly doesn't seem to match the pattern most people report here.
And all of this happened in a relatively mild evening. Although, it was particularly warm the week before and the car lives its whole life grilling out in the sun. People love our "great" weather, but personally I despise the summers here.

Perhaps some soldered joint was hanging on for dear life after countless heat cycles and finally decided to let go.
Or, maybe all the humidity evaporated before I could see it.

I'll definitely look to clean all drains thoroughly and apply the heatsink upgrade.
Can the black plastic cover on the top of the CEM just be pried off to access the other half of the PCB? I'm always weary of applying "too much" force to brittle 24 year old plastics.
I also found the large connector ungodly difficult to remove, I was close to giving up when it finally came off.

[hiroku]

So last week my "new" CEM arrived in the mail.
I had it repaired by Erich Technical Support in the Netherlands (https://www.ets1.nl/).

As my module was completely bricked, he pulled the memory chip out, back up the data, copied it into a new chip, and put that into a new CEM.
Received my new CEM the next day, installed it on the car, put all the relays back, and all is fine just as it was before.
It even comes with a nice like 12-volt fan built-in. It's very quiet and overall an elegant solution for future overheating problems. You do have to cut an opening in the relay housing for airflow, I used a mini-dremel.
It's still a mistery what exactly went bad with the old unit.

For anyone with similar issues, I highly recommend Frans' work. His communication was top notch, the CEM was diagnosed, repaired and shipped back within one day, and the overall quality of the repair is excellent. The price was also more than fair.