Can-bus guru's advice needed please. Topic is solved

[yagger]

Free2drive!, actually, cars 2004 MY have standart problem like bad CEM, unfortunatly. But, for sure, need add information about your car, and better if you will do some thing following some instructions real time. jimmy57 wrote correct about check CAN, but there are many other details, you need to understand it.
Volvo consist difficult electronic system, and for fix some problems not enough check some wires, sometimes temporary need to replace some modules or sensors for check. Dealer cant do it, because they follow rules, and they, if need, replace modules to new thing only.

[yagger]

Can a single component failure wipe out the CANBUS protocol?

Yes. CAN bus is 2 wires, via it modules communicate each other. If inside one from all modules get short circuit, this 2 wires will looks like 1 wire, that not enough for communicate to use differential signal CAN bus.

[Free2drive!]

Yagger, very helpful explanation of can-bus. Thanks!

Second CEM replacement arrived yesterday morning. It's fitted and car is working again with no messages on the DIM.

Since cleaning the ground points in the engine bay the car starts instantly. Maybe voltage drops or spikes were knocking out the CEM, I don't know.

I'm not convinced it's going to last but it is running very well with no thuds in the transmission and no random lights etc.

I will keep you all posted, I'll give it a month or so before declaring it 'solved'.
Matthew

[Free2drive!]

Hello Everyone

Well so far so good, car is running fine.

Work done to resolve the issues in the first post.
New battery
Alternator test
Removed and cleaned starter motor and alternator connections.
Removed and cleaned earth points on both front wings, A pillar, and under rear seats.
Removed main earth strap (was finger tight at connection to engine block).
Removed wiring for very early hands free phone kit. Previous owner had cut wires and left them bare ended, which I'm told may cause ground issues or confusion in the can-bus.
Replaced CEM with a repaired one.
I wasn't able to replicate any of the issues and I didn't get confirmation on whether the first repaired CEM had failed or not. So I'm not 100% certain the issue is sorted.

It's running fine again.

I'm happy and grateful to everyone who read and contributed to this post.
Thanks MVS for your help.
Mattt

[abscate]

That user installed phone kit probably took out your CEM, my guess

[Free2drive!]

Thanks Abscate,
Very likely. But how would it do that intermittently? Why wouldn't it blow a fuse instead of taking out the CEM?
Matt

[abscate]

If you had loose wires they could easily pick up,electrical noise and put noise onto the CANBUS circuit.

I need to subscribe to Yagger and jimmys posts...I always learn something from them

[yagger]

You forgot about Doublebug )))

[abscate]

You forgot about Doublebug )))

Always learning from your posts!!



I did forget Henry, too.

[Free2drive!]

Bad news! It's all started again.

Saturday - anti skid
Sunday - anti skid then brake stop safely
Today - antiskid/brake stop safely then clunk into limp mode.
It drove fine an hour later. It will fail to start soon and I'm back to square one.

I'm told something on the system is sending corrupted information but what?

I'm keen to solve this with logical steps please give me advice.
Thanks in advance
Matt