CEM related issues: My diary of ongoing findings...
 

Chaps,

I've been posting on a couple of Facebook pages but such is the joy of that format, keeping a thread going is no mean feat so just putting this here to a) document things for my benefit and b) hopefully seek some words of wisdom.

The issue:

I have a 2007 V50 2.0 Sport that I've owned coming on for 2 years now and it's a fabulous thing that I love and despite its 218,000 miles it's behaving (largely) very well however about 6 months in to ownership, out of the blue one day it had an electrical meltdown with her ladyship at the wheel.

Loss of power
Wipers running themselves
Brake failure - Stop immediately warning
ABS / DSTC light on
Radio / heater panel erratic

Now, I was aware of the S40 / V50 CEM related problems and knew that Volvo's stance was to simply replace all of the above, reprogramme it and job's a good un however I also knew that the pins / multi-plugs could cause issues and cleaning them usually works.

So, I unplugged all the plugs and removed the CEM and carefully cleaned the pins with electrical contact cleaner and then sprayed the multi-plugs and all was well, issues resolved and the car drove perfectly for weeks, maybe even months and peace was restored to the household.

Spoke too soon...

Around last November, it happened again... exact same symptoms and turning the car on and off didn't change anything. Wife en route to an interview... temper lost. At the roadside I unplugged the multi-plugs, plugged them back in and away it went again, driving perfectly and did so for another few weeks... then did it again. But again, unplug, plug in and away it went again.

So, by this stage I'd started looking into the many many posts on the subject and they all seemed to end with "clean the pins" and that was it, problem solved but I wasn't sure on that one as the pins on mine were clean, free from corrosion and wiggling, poking and prodding when the car was running has no ill effect on matters. It was and still is, a completely sporadic issue. I did happen across a thread where a chap seemed to think that one of the snap lock clamps was worn and thus wasn't holding the corresponding plug tightly in place so I checked all of mine and all seemed well.

Still with me...?

Before Christmas, it happened again and like the previous times there was no common reason... it didn't seem to matter of it was hot, cold, wet or dry and nor could I see any reasons for it doing what it did though Googling seemed to hint at leaking windscreens or dodgy sunroof drains being a prime suspect in introducing moisture in to the car and thus, in to the CEM itself but I was pretty confident mine wasn't suffering from any moisture and kicked, nudging and shaking the CEM whilst in motion did nothing thus I ruled out an errant handbag or bottle of wine rolling around the footwell.

The last time it happened, I didn't unplug all the multi-plugs but instead ONLY unplugged the tow smaller ones (green and brown) on the base of the unit and plugged them in. Again, issue resolved which made me wonder if I'd started to home in on the culprit. I again painstakingly cleaned the terminal and pins and added a thin strip of cloth tape to the sides of the multi-plugs to try and ensure there were very snug in their place in the CEM and then put a strip of duct tape over the top to hold both plugs tightly in.

Problem solved...

Or so I thought as it ran fine for the past 6 weeks / 2,000 miles however yesterday it did it again en route to my wife's work and having somehow manged to get it there, she called at 5pm to say the car would not start. It was "dead" and so she'd had enough and got a lift. Part of me hoped it was dead as fault finding may have just got a bit easier.

Alas, I was wrong and today I went to collect it and whilst the doors unlocked, the dash fired in to life and the key slot "clicked" to accept the key... there was nothing. Key out, back in and it started first turn and did so for several repeated attempts. No lights on the dash, no warnings, no mad wipers. I left it and returned an hour or so later and it started first turn however immediately went into meltdown without even being moved. Again, unplugged the small green plug, re-plugged and away it went happily.

**** got serious...

Once home, I removed the CEM completely and took the circuit board out of the plastic housing (having removed all the fuses and relays) and on inspection, there is no evidence of any corrosion what-so-ever nor any moisture which confirms my suspicions that my issues aren't moisture or corrosion related. However, with the unit laid bare I cleaned ever single pin so it was showing the bronze coloured metal (thus absolutely no buildup on the pins) and cleaned every fuse before refitting and then doused in contact cleaner, blew out with the airline and likewise on the multi-plugs and refitted and needless to say, all is well but is it fixed... will it do it again next week... or next month?

There lies the issue... every time I remove the plugs and reconnect, it's fixed and it'll run flawlessly for however long it likes then without warning, will have a meltdown... or perhaps it won't now but the issue being, she's lost all faith and wants rid of it. And probably me as I'm still fighting its case much to her disgust and I can see why she's unhappy, toddler in the car, lone female... rural living and an issue that seems impossible to trace.

My options...

Well, that's the reason for this post as hypothetically it may be fixed now but the chances are I'll be back soon to say "Guess what, done it again" and so having put it out there, I'd be keen for any advice / words of wisdom / previous victims and more so, if anybody found a solution.

I know that used CEM's have to be coded to work, though there seems to be a debate over whether used CEM's can be re-coded for the immobilser and such like - any ideas?

Volvo Diagnostics do a refurbished CEM for £260.00 which is plug and play, thus I assume your old one goes off to them first to be cloned over and whilst that seems the best option and I've a very high opinion of their work (they did a DEM on a V70R for me) the issue is... I'm honestly not convinced it's the CEM itself to blame.

Volvo do a replacement pin set for the multi-plugs but they thought of trying to re-pin eight multi-plugs does not inspire me plus I'm reliably informed, it's rather costly too plus part of me thinks how would that resolve the issue... issue possibly being a poor connection but you'd expect some sort of glitch as the wires were pulled about with the car running, but there's not.

Finally, somebody suggested electrically conductive grease but again the jury is out as to how effective it would be but anything is worth trying I guess.

Sell it, buy her a VW Up! GTi...

Yes, that'd be a solution but I'm now so ****ed with this and the fact that I'm unable to hone in on the source of the issues, that I want to see it through. For such a common issue, there's very little in the way of resolution... I mean is there a common issue or does this sound unique given I've done the usual tried and tested suggestions and yet the fault keeps recurring.

Open to any and all suggestions and happy to discuss this further / share my findings moving forwards...

Cheers

Hi - thanks for the interesting post. I’m fortunate enough to not have been affected by these issues (...yet...?), but I am an automotive electronics engineer so hopefully I can provide some useful input.

If we assume the CEM itself is not faulty, to cause such widespread issues it’s likely that either the power supply, or CAN or LIN networks are the connections which are suffering.

Although I don’t know which pins these are, it should narrow down which connections you need to concentrate on if you can find out.

Sounds like pin connectivity issues.

The pins may not have enough contact pressure and then vibration and heat means that one or more pins may loose contact momentarily.
The impact may be nil, trivial, or major, depending on what the pin is and what it carries.

Solution: increase the contact pressure through following means:
1. New pins (the best most reliable method, but takes longest to fit)
2. Gently and delicately deform the pin to make it more snug. The cheap and poor mans method, may last a lifetime, may not...

This has been going on for over 10 years now occasionally on random S40/V50/C70 / C30 cars , every dealer should know what to do by now .

There are three twisted pairs of digital network communication wires going to the CEM through different plugs , the female terminals in the plugs fret and loose their grip on the CEM pins , volvo do the repair terminals . By rubbing the protective tin off the cem pins you are going to make things even worse .

Thanks gents, pretty much confirmed my suspicions that it's a problem at the multiplug and I suspect it's either or both the small green plug or small brown plug on the underside of the CEM.

I'd actually like it to get worse, mightier easier to pin point the problem but for now, needless to say it's running fine again... which has impressed my wife. And I quote "Well, you must be f*cking magic as it doesn't work for me"

I may go for the careful manipulation of the pins idea, assuming I can narrow down the likely suspects. Repinning the plugs sounds expensive and problem beyond my skill set too.

I'll away and research the contents of the last posts and go from there.

Much obliged gents

Well written post Turbodave, nice and easy to read and clearly explained.

Clan's advice sounds spot on, replacing the female terminals of a multi-plug sounds very fiddly to me; is this something a competent (and patient) DIY'er could perform at home and in-situ within the footwell area :speechless-smiley-5

Tempting fate but I've never had an issue with my CEM in 11 years, although the plugs have never been disconnected. I guess the more times you plug/unplug the 'looser' the connections.

On the other hand each time you take them out it scrapes them clean , it is a damp area down there with passenger's wet feet . The vast majority don't have any problems but unfortunate a few do , but it is known now what is going on👍

I ended up purchasing a recon CEM from Volvo diagnostic. I gave them the old one and they transferred the software onto the recon CEM in 45 mins. The CEM has been back on over 6 weeks now with no issues. The old CEM showed no sign of corrosion and the "clean the pins and spray the connectors" worked a few times but I was getting fed up with the "brake failure message" especially on the motorway at high speed. Fingers crossed I'm free of any more CEM issues!

Just to update this...

Since my first post and having removed the CEM completely, split it and gently filed the pins with the wife's foam backed nail file and then cleaned the board, the pins and the multi-plugs (again) with contact cleaner and a toothbrush, reassembled, cleared the codes... a couple of months and about 5,000 miles have passed and thus far, it's been fine with no CEM related issues to report.

Granted, I've probably now jinxed it and it'll pack in tomorrow but given it was giving issues on a fairly regular basis, whilst I can't say it's fixed fixed, it certainly appears better. Whether it was filing the pins or another clean or the plugs / pins are sitting better or all of the above, who knows...

Until it happens again, I'm not inclined to start fiddling with it again.

Watch this space...

:omg_smile:

I have had this problem on my C70 but am currently "in remission". If and when it comes back I will be very tempted to bypass the plugs altogether with soldered wire bridges, if indeed I am able to identify just 6 wires (3x twisted pairs) carrying the digital comms.