S40 V40: CEM Wiring/Repair Information

[gatos]

Originally Posted by baldmosher

That is cool. I am likely to try and set up a VM on my laptop as someone else has recommended it but I'll get in touch with RobbieH!

I am using Oracle's VM Virtualbox to run Windows XP Pro on my Linux based laptop and it's perfect

[hart1mart]

Hi everyone was wondering if someone would be kind enough to help me out, I have a Volvo v40 D Sport 2002 model, I have read the entire posts concerning the CEM and think this could be the problem. I would like to have a go at trying a fix it. The problem is all lights were working fine until yesterday; I have lost side lights rear lights, licence plate light. All other lights front, hazards & main beam are all working fine. Can anyone tell me what relay controls the rear lights please, much appreciation to anyone who can point me the right direction. Many thanks in advance, Martin.

[baldmosher]

I don't know for sure, but that sounds more like a blown fuse... which in turn could imply a faulty wiring loom.... probably more likely if yours is a Phase 1 than a Phase 2 simply because of age. Have you checked the two fuse boxes first (I've no idea which fuses it'll be but no doubt there will be threads on here)? Replacing that might get you going at least although no telling if it'll pop again next time it rains.

If there is a CEM relay that controls all those lamps, then be warned that the solder is coated with some kind of anti-melt coating which means you'll have a right job removing the old solder. It's doable but it's a right faff, or so The Wife™ tells me, she does all the soldering around these parts.

[gerowr]

Originally Posted by Russell_S

Hi, I've recently had a headlight problem which, at first, appeared to be the common CEM issue (see this thread http://www.volvoforums.org.uk/showthread.php?t=67437) but finally turned out to be a break in the wiring loom. However, while fault finding the problem I found out a bit about the CEM which I thought others could find useful in faulfinding their own headlight related issues. I've taken a few pictures to help with this.

I have attached to this thread the Volvo wiring diagram for the CEM and headlights because the Haynes manual is worse than useless in this respect as it doesn't even show the CEM in their wiring diagrams.
I have also attached the data sheet for the Fujitsu relays that are used for the headlight switching in the CEM. I originally assumed that they would be solid state relays but in fact they are normal miniature PCB mounting mechanical relays so it they do fail then the data sheet could help find a replacement to repair the CEM.

Firstly, for those who don't know where the Central Electronics Module (CEM) is situated, here is a picture:



Next we have a picture of the CEM circuit board itself highlighting the headlight relays:



and now a picture of the CEM connectors and their pin numbering to go with the attached wiring diagram:



Hopefully others will find this information useful as the CEM does appear to be a weak component with respect to headlight switching.


Regards

Russell

I have just joined the Volvo forum and found information for use on my 2003 S40 with headlight problems. I found good info, but I cannot open the attached pdf files for some reason. The file opens showing only the link info and never opens or downloads the pdf file. What am I doing wrong? What I reall y need is the wiring diagram from the CEM module to right and left low beam lights. Thanks.

[v40alex]

You're not doing anything wrong, the forum moved to a new server but unfortunately attachments couldn't come for the ride.

2003
http://www.volvowiringdiagrams.com/v...20Diagrams.pdf

[Rossc0]

So I've done some investigating into my problem. I bought another CEM from the local scrapyard for £5, plugged it in but no joy. Started prodding with a power probe, probing the wire for the blown headlight, as it comes from the CEM makes the light illuminate. So surely can't be broken wires. I'm assuming I've got another dud CEM. Anyone got a CEM ending in 305 for sale ASAP?

[Rossc0]

Bought a working CEM, still no luck.
Any ideas? I'm stumped

[v40alex]

Did you do your voltmeter tests? I'd check the wiring that goes under the radiator - it's a known point of corrosion.

[Rossc0]

Originally Posted by v40alex

Did you do your voltmeter tests? I'd check the wiring that goes under the radiator - it's a known point of corrosion.

But if that was knackered then me putting power through the wire that comes out from the CEM (putting power probe into the wire right behind the plug for CEM) surely wouldnt light up the headlight bulb like it did.
Also my full beam has now gone too

[baldmosher]

It's not the wiring going INTO the CEM shorting out is it? Maybe try a new stalk or headlight switch unit perhaps?

I've got a left hand stalk spare if you want to try it, £10 posted, if it doesn't solve the issue then just keep it as a spare or put it on eBay. NB: I can't actually remember if it's the left or right stalk that flashes the headlights