Electrics: Wipers suddenly stopped working

[moleadrian]

Sadly, after many months of ownership of our 2005 (55) XC90 Ocean Race, the wipers for no reason stopped working whilst sailing along the m54 in some awful weather conditions. Although I did manage to get to my destination, I was unable to find a cause for the fault and on my return I've been through the car from back to front checking fuses, relays and earthing points etc, but still unable to get the wipers working. Currently I have a temporary cable running from the earth terminal of the wiper relay to earth (via a switch in the cabin), just so I can legally use the car. Has anyone else had this issue? is it likely to be CEM related? as this appears to control the relays grounding, also can the CEM be swapped out and plug'n'play with another XC90 CEM?

[Moose Test]

I don't profess to be a "CEM expert" but my understanding is that this is not a trivial matter and certainly not a plug-n-play one.

For starters, the CEM maintains a permanent mileage record for the vehicle. If you could directly replace it with another, a discrepancy will be detected with the mileage value recorded in the DIM. Fun ensues.

Also, certain system modules have their serial numbers / identities stored in the CEM and will be denied access to the affected bus (e.g. audio modules on the MOST bus).

It is my current understanding that a replacement with a breaker part is possible but you essentially require a unit of the same model year, pretty much the same original part number, and some reprogramming is still going to be required.

Regarding your specific symptoms, do the wipers work in any mode at all? High/Low/Intermittent/Auto? The wiring diagram for that MY depicts two relays, with separate current sink lines on the CEM.

[gmonag]

the wipers for no reason stopped working

I doubt that. There is always a reason, you just have to find it, then think about what to replace.

[moleadrian]

Originally Posted by Moose Test

I don't profess to be a "CEM expert" but my understanding is that this is not a trivial matter and certainly not a plug-n-play one.

For starters, the CEM maintains a permanent mileage record for the vehicle. If you could directly replace it with another, a discrepancy will be detected with the mileage value recorded in the DIM. Fun ensues.

Also, certain system modules have their serial numbers / identities stored in the CEM and will be denied access to the affected bus (e.g. audio modules on the MOST bus).

It is my current understanding that a replacement with a breaker part is possible but you essentially require a unit of the same model year, pretty much the same original part number, and some reprogramming is still going to be required.

Regarding your specific symptoms, do the wipers work in any mode at all? High/Low/Intermittent/Auto? The wiring diagram for that MY depicts two relays, with separate current sink lines on the CEM.

the wipers don't work in any mode, but the stalk will still wash the front windscreen and do all the rear functions, the front motor works but you have to trick it into working, I swapped the 3 wash/wipe relays about the 3 sockets but no difference to any wash wipe operation, so that rules that out afaik

Originally Posted by gmonag

I doubt that. There is always a reason, you just have to find it, then think about what to replace.

constructive ??? I think I have covered all the bases, bar the CEM and the SWM, I stripped and rebuild the wiper motor and then fuly tested it, I also swapped out the wiper stalk, the rest is computer based or the links between, that is a much harder job to pin down, even with a multimeter, but thanks for your input.

[Moose Test]

Given that the intermittent/auto and continuous wipe functions operate through independent relays and CEM signal paths, and that you can get the wipers to operate by providing an external return path which bypasses the CEM, I'm inclined to suspect a CEM fault. Either that, or there is a wiring fault in the loom between the CEM and relay sockets.

I think it is worth bearing in mind that you say the fault developed during "awful weather conditions", and that early models are known for the possibility of water ingress into the CEM via deficient bulkhead seals, causing corrosion and damage. Do all the vehicle's other systems function as expected? Are there any signs of dampness in or around the driver's footwell?

If it were me, I'd take it to a Volvo dealership. Part of their standard workshop equipment are CEM breakout boxes which make access to the relevant wiring easier and allow testing whilst the system is fully powered up and operational.

Good luck with it, I hope for you that it isn't the CEM.

[gmonag]

constructive ???

I was being constructive. You are talking about swapping the CEM on a whim!

Diagnose, then replace parts

[moleadrian]

Originally Posted by Moose Test

Given that the intermittent/auto and continuous wipe functions operate through independent relays and CEM signal paths, and that you can get the wipers to operate by providing an external return path which bypasses the CEM, I'm inclined to suspect a CEM fault. Either that, or there is a wiring fault in the loom between the CEM and relay sockets.

I think it is worth bearing in mind that you say the fault developed during "awful weather conditions", and that early models are known for the possibility of water ingress into the CEM via deficient bulkhead seals, causing corrosion and damage. Do all the vehicle's other systems function as expected? Are there any signs of dampness in or around the driver's footwell?

If it were me, I'd take it to a Volvo dealership. Part of their standard workshop equipment are CEM breakout boxes which make access to the relevant wiring easier and allow testing whilst the system is fully powered up and operational.

Good luck with it, I hope for you that it isn't the CEM.

It's looking like you mention, as the XC90 has a nastily designed wiring tray that runs across the scuttle panel, it looked mucky and wet. It did log in my head as a possible cause of trouble, but time now to dry out and dig a little deeper.....thanks

Originally Posted by gmonag

I was being constructive. You are talking about swapping the CEM on a whim!

Diagnose, then replace parts

Constructive.......above is a beautifully crafted constructive reply.....take note and learn.....as that is all I'm trying to do...thank you

[volvo for ever]

if uses are okay then remove wiper arms x2 then scuttle panel inspevt green or blue plug top of cem for water contamination .

ive had this before where wipers just packed in my05 xc90 also look at recent weather weve had

regards.

[xc90me]

I know this is an older post, but I recently purchased a 2005 xc90 T5 that seems to have the same issue. I have verified no power is getting to the wiper motor, but all other functions seem to work on the wiper stick (just as you indicated above)

I was wondering what your resolution was - I'm thinking of having my CEM sent out for reprogramming. In addition to wipers not working, I have had intermittent problems with the tail lights going out and turn signals indicating bulb failures. Shutting off the car for a minute or so usually resolves the intermittent issues, but the wipers still won't work. So, if you are still active on the board, I would appreciate knowing how it all worked out for you.

Thanks