CEM Wiring/Repair Information
 

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:
http://i93.photobucket.com/albums/l7...EMLocation.jpg


Next we have a picture of the CEM circuit board itself highlighting the headlight relays:
http://i93.photobucket.com/albums/l7...MPCBRelays.jpg


and now a picture of the CEM connectors and their pin numbering to go with the attached wiring diagram:
http://i93.photobucket.com/albums/l7...Connectors.jpg


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


Regards

Russell

Wow- thanks for the info. Always wondered how the headlights knew to dim when starting the engine - a clever box of tricks until it goes wrong. Think l'll be paying a trip to the scrappy before attemting repair of a CEM!

Does anybody know anyone who can repair CEMs if they have a relay problem? But thanks for the post.

Got a headlight problem with mine. Don't know what it is though or how to fault find any more than I already have. No voltage on the left side head light, only getting about 1.3v at the fuse box. Right hand headlight fine. Side lights fine. Full beam fine on both sides. Anyone got any more suggestions or do I need to take it to the garage. Cheers

I wonder if this unit can be altered to turn off the DRL's :P

Oh bu**er!

O/S dipped head light not on (I use DRL's). Did the normal, changed the bulb, no joy.

Checked the fuses, relays and had a look at the loom (under the radiator) with no fault found.

Had the car in for some other work and they traced the defect to the CEM. Glad I was sitting down when the service guy rang me to give me the "good news" - along with the cost of a replacment new unit + labour for fault finding and replacement + (of course!) Darling's 15%!

Of course the bloody light is working fine now! Agree that Haynes is as much use as a chocolate fire guard, but if I get a repeat of this fault I'll know where to look!

Thanks for the post, headlight dip light doesn't work. trace the problem back to one of the relay in the CEM, VOLVO quote 400 plus for the whole CEM unit. Scrap yard 50 pounds. But you can also buy the Fujitsu relay as a component from sales@inelcohunter.co.uk. not too sure how much each relay cost, because i managed to repair the faulty relay (due to dry joint).

I do agree that the Haynes manual is useless!

Did someone know, which of this is the rear wiper relay?

......the relay is in the cabin fusebox as pic....don`t know what year or model yours is but i expect it is in the same place....

Thank you for your picture, I really want this VADIS :-)

Unfortunatly the wiper relay has to be located in the CEM in my car model, the location you showed was in previous models though.

My car is a year 2000 (march) model and something between phase I and phase II.

Not shure whater VADIS knows what inside the CEM, but it would realy help!

...Vadis says it is in the same place on a V40 2001...read the model and year at the top....the CEM is changed as a unit with no pics. of the inside...2004 is the same...

Brilliant
 

Thank you for posting this and the photos, went to scrappy today got CEM and now have headlights £47 total.

tidy
 

going to get the alloys of it as well

Can anyone help me? I have a 98 'S' S40, and I'm trying to locate the headlight relay. After looking at the picutres and almost breaking my back trying to get my head in the footwell, I don't have the same box of tricks there. I can't seem to find my CEM, or th headlight relay. If anyone can help me locate it, that would be fantastic and its had me scratching my head for days now!

Had a quick look on Vadis for a 1998 car and it seems to be at the same place. Silly question, but have you removed the lower driver's side protector panel?

Wattsys40, If you need one, I have a spare one for sale by the way. That is if you find where yours is first. :)

Thanks for looking, if you mean the panel that sides left of the bonnet release then yes I have, but all that is there is a keyless entry box and another little box, but none of it looked like the picture. If I get a change, I'll get out there and take a picture. Thanks for your help though, most appriciated.

I've just bought a second hand S40 1.8iXS with 36k miles and the paperwork with it shows that its had a new CEM because the headlamp bulbs were blowing. A common fault then.

I just got a nearside lamp out, and the heat has burned through the wiring and 3 spade plastic plug that connects to the bulb.

Gotta do some investigation first, but if I need a CEM, whats your price for your spare, posted to Wolves?

fog lights
 

Does this controll the fog lights in my 96 S40, does anyone know where the relay is located for the front fog lights or what item number it is Haynes and sidaV are useless!

I would suggest you check your PARKING LAMPS and POSITION lamps fuses in the engine compartment. One of them, I can't remember which one, had a fuse blown and apparently it was affecting front and rear fog lights. When i replaced that fuse I got both fog lights on the front and the one on the back working fine. Very odd as the Fog lights fuse was fine.

Thanks for the very useful information, Russell_S.

In my case, I have a V40 which had a failed LH dipped beam. The light was on if the engine was running and off if the engine stopped (all switches were on). Finally, this was traced to a problem with the relay on the CEM board. When the engine is on, the control voltage on the relay is about 13V, which is high enough to activate the old relay. When off, the battery voltage is about 11.5V, so the relay does not move at all.

The problem is definately with the relay. But to get a replacement relay is not easy. Dealers do not have the relay as a component but would charge about £450 for the whole CEM. In the end, I found a replacement from RS (stock number 217-2876) and only costs £1.47 plus VAT and del.

Link here:
http://uk.rs-online.com/web/search/s...7-2876&x=0&y=0

I have also attached the datasheet here. It is 15A compared with the old 20A, but well enough for the dipped beam (about 5A).

After replaced with the new relay, my V40 returns to normal.

hey qipan, you said yours was the ls, and that was the replacement relay for it.


will that same relay be ok for the right side light?


cheers andy

Hi All,

Great info, priceless.

The other relays in there, are they for fog lights?

I'm trying to retrofit front foglights and want to know if there's anything else I'll need.

Many Thanks,

Daniel.

Hi Andy

From the picture of the CEM board, it appears that they are of the same type relay with the same part number on the body and so I think it should be okay for the RH side too.

great stuff qipan

one last thing, does a phase 1 cem fit on a phase two cem, aand vice versa.


cheers

Sorry I have no idea. My V40 is 2000 GDI model, and the engine has the fly-by-wire type throttle. The CEM board is just like the picture shown at the beginning of the thread.

Probably you can check up with your local Volvo dealer parts to find out. After all the advice/info from them is free!

XC90 CEM - Xenon probs
 

Hi, I have an XC90 (2003). My passenger side xenon dipped beam flicks on and off whilst I'm driving, sometimes it stays on for a whole journey other times it is on and off every 30 seconds, I've also got water coming into the cabin from somewhere (it's under the floor near the yaw sensor).

Just wondering if these things can all be linked. I'm really scratching my head with this one. I've posted under the proper forum section my problem but saw this thread whilst searching for an answer and just thought I would ask?

regards, Jim.

Hi Jim

I think you can do a quick test to see if the problem comes from the relay.

Switch on ALL lights but without turning the engine on (this will set a lower battery voltage to the relay), check if the faulty light is on. Then turn the engine on (set a higher voltage) and check the light again.

If the light is off when the engine is not running and on (or sometime on) when the engine is running, it is almost certain that the relay is faulty.

If the light is on in both cases, it may be something esle like bad contacts etc.

Quick test
 

I have tried the test and my lights light up all the time, just seems to be whilst driving they cut out, does this point to a bulb or igniter failure?

Does anyone know if the CEM controls the sidelights? I have a 2000 V40 1.8 XS and none of the sidelights are working. Hubby says he has checked fuses and bulbs and says he can hear a relay clicking and is wondering if the CEM isnt sending power to any of the sidelights for some reason? (Headlights work if the switch is in position 0 and in headlights on position, both with engine on and off but no sidelights at all.)

So it is inconclusive. Do not think it is due to the bulb but I could be wrong.

Maybe you can try cleaning the electrcial contacts of the light by using some electronic cleaning solvent (not the mechanic type like WD40). I have used it to clean the door light switch to make it work again.

Are you sure the relay is working fine? I have a 2001 V40 1.8 which had a failed LH dipped beam. I knew the relay would be faulty when I read this topic, but it seemed to work when I tested it. I mean, there was around 12 V voltage when lights were turned on and zero voltage when lights were off. It looked like the relay would be OK (you could have heard a clicking sound if you had decent hearing), but still, there was no light. It somehow limited the current in such a way that it was not able to turn the light on. The relay may be faulty even if it seemed to be ok.

In my case, I fixed the lights by replacing the relay with about similar one.

Very useful info, thanks!

Was it easy to replace the relay on the circuit board? What tools did you use?

I have heard of this water problem from a local volvo specialist, if i remember the water comes in somehere round the handbrake cable, which in turn rusts and snaps. Seem to remember him saying he,d seen a few with a fair bit of water under the carpets. Hope this helps. If you need mor info pm me.

Was easy for me as I do soldering regularly. Maybe a bit tricky if no experience before.

Anyway I used a slightly bigger soldering iron tip (electronics tool) and some solder wick to absorb the solder as much as possible off the relay pins. And then gradually loose the pins inside pcb holes and gently pull the relay out while heat the pins at the same time. Once out of the board, it is easy enough to put a new one on. Good luck.

V40 Headlight Beam Fix
 

Hi, thought I would update this thread as the information posted above was a huge help providing me the information needed to repair my CEM. I have a V40DS on a '51 plate and the nearside dipped headlight beam would sometimes work and sometimes not, this had no real pattern whether ignition was on or off. I removed the CEM from the plastic enclosure and plugged it into the car as a bare board and when I found the headlight not on, flicking the corner of the board would force it on everytime. I ordered the above relays (£1.74 plus VAT + Shipping - 2 relays will actually cost you about £9.50 as the shipping is next day at £4.95). Desoldered the old relay and installed the new one and now the headlight is working perfectly.

Thanks again for the help and confirmation this procedure was correct for my circumstances as above.

Well, it happen to one of our fellow volvo owner, who happens to know about electronics too. He soldered new relay in place and it worked. Later, he went to analyse the old relay part. He took it apart. Guess what he found - inside was another, smaller relay, soldered to pins of outer shell. How amazing is that ?!?!

yes , just read your owner's handbook :-)