V50 CEM problem? What to do next?
 

Right, yesterday I removed the CEM from my 2004 V50 (T5 AWD version) from under the glove box, disassembled it and contact cleaned it and put it back together.

Why? Because I've been getting the brake failure, pull over safety message which puts the car into limp mode. Incidentally the indicators stop working when this happens which makes it dangerous even to pull over. Feels like an electrical fault to me?

I have read this useful thread: https://www.volvoforums.org.uk/showthread.php?t=302607 as a starting point.

As soon as I started it back up the message appeared again, whereas it used at least to take a bit of driving to trigger it!

I took it to my local volvo specialist who plugged it in but said that he couldn't get a signal through the rear diff at all which hindered his dianostic efforts. He says he can't repair the diff or or get it refurbished because its too rare, being the Awd T5 version which are like hen's teeth in the UK. A more common volvo like a v60 say he'd have no problem getting the diff refurbished for a reasonable price and then he could continue with the diagnosis. A new one costs £££s.

This has put paid to his diagnostic efforts so I'm stuck with a car I can't drive at the moment. Car still has plenty of life in it so reluctant to ditch it just yet.

Any ideas?

start with that
6 leads from the main dealer and a bit of fitting time
(part numbers further along in the thread)

Either find a Decent Indy who has Vida + Dice to read the car Correctly
Buy yourself a setup and diy ( https://www.volvoforums.org.uk/showthread.php?t=253191 )

use the contents of the swear jar to fund whichever option suits you

Hi
2005 AWD owner here. Yea, getting help from any garage for our cars specific parts may be tricky indeed, but im not sure how much your mech is knowledgeable in P1 AWD platform and how much its just "standard diagnostic equipment seem not to see haldex controller" ?
Starting from basic - as above, yes you need yourself or someone with Vida+Dice , thats your first step. The amount of problems it can sort is insane and sometimnes even best garage diagnostic tool can lead you towards wrong conclusions with our cars, seen this before.
"repairing diff" indeed seem problematic but its usually haldex CONTROLLER not diff that will cayse lack of connection issue. Haldex controllers actually are possible to find in EU markets where AWD was much more popular or in US. You can even try to retrofit gen3 controller from XC90V8 (tried myself, failed twice, gave up ) so there are more options than just your exact part number. Also those controllers rarely give up, usually its the internal colenoids or something but full module? possible yes, but I would double check it with Vida+Dice unless your mech has that?
lastly - I heard of few T5AWDs with not working haldex and apart from being perfectly fine FWD cars those didnt cause problems, unless brake failure message is caused by more sinister problem, it may actually not affect you as much until you find controller to replace?
anyway - if I can help anything with AWD related questions, fire away, had my share of issues with my dear pig :) for last 5years+ so may come across some of your problems.

Hi. I saw that but for the life of me couldn't see the three twisted wires spoken about? I could see one- going into a small black unit of the ECU, but no others. Are they buried deep inside the multi cable bundles of wires? If/when I do find them is it a matter of splicing new bits of cable onto the existing ones?

To the conversation generally I'm pretty sure that the garage has full diagnostic equipment since they are an independent Volvo specialist but they seemed to call it a day when they couldn't get continuity through the rear diff. I have a sneaking feeling that the rear diff is fine and it is an electrical issue.

I do have a page and a half of a printout from the diagnostic.

thats exactly what I was pointing out - haldex controller is a "electrical box" that engages haldex clutch when needed to send power to rear diff that is a mechanical contraption with some gears and fluid. When our cars "loose AWD ability" its usually because haldex controller packs up in some way or not getting proper info to engage itself (ie lack of info from CEM that front wheels are spinning). If it "packs up" you usually see warning on dash saying something is wrong etc.
From what I experienced, its more possible the problem is in the controller itself rather than in CEM or rear diff but its just my 2c.

Thanks.
How could I check whether the rear wheels are being driven?

Seems like I need to find these twisted wires as mentioned above- has anyone any guidance on where to look!

check the haldex controler for water ingress

easiest way - turn off DSTC and floor it from standstill on wet(ish). If AWD is working, you will catapult nicely, if it isnt, you will feel it with torque steer and insane front wheel spin.

Also more scientific test :

1) lift the car up all 4 wheels
2) start it up, put in 1st gear, leave it running with wheel spinning freely

-all 4 wheels should spin (that however doesnt mean haldex is working correctly)

3) stop one of the rear wheels with hand (there will be no resistance as it has open dif)
- rear wheel on other side will continue to spin

4) now the important bit - if haldex controller is NON operational , you will be able to stop that other rear wheel withg your hand easily (no resistance)
If haldex IS OPERATIONAL, you WONT be able to stop that other wheel from rolling using your hands.

obv be careful when doing so and dont put your hands in alloy spikes, just do it with gloves and touich the outside of tyre.

Given the symptoms came back as soon as it was started, is it possible that you've disturbed something loom / CEM related but not in a good way? Possible bent a pin/s etc or a multi-plug not pushed home. Have you tried the slightly basic "unplug it, plug it in again" just in case somethings not sat correctly.

As an aside, I started said linked to thread and appear to have been very fortunate as following months of sporadic and unpredictable issues, my somewhat frowned up "fix" has held up fine (touch wood) and I'm another year down the line with temperatures from -12degs to 28degs and lots of not being careful around the CEM area and touch wood, no recurring issues.

Hi Turbodave.

I don't think I've bent anything but I'm certainly going to attempt a repeat of the whole procedure.

Can you help as to where these darned twisted wires ARE? I can't see them (well, I can see one that fits the bill)- do I have to remove the cable ties from around the bundles of wires and have a root around inside?