Another Headlight Issue

[Russell_S]

Hi, hopefully someone can give me some guidance here regarding my 2002 S40.

The other day my O/S dipped headlight stopped working and I naturally thought it was just a blown bulb (regular occurrence). Anyway, tonight I went to change the bulb and found that it hadn't blown after all. So, I've measured the voltages and found that with the headlight connector disconnected from the bulb I only get about 10v on the red wire whereas on the N/S one I get about 14v (when disconnected from bulb). However, if I connect the faulty side back up again the voltage drops to 0v on the red wire. The diagram in the Haynes manual bears no resemblance to the headlight wiring in my car at all.

Anyway, I gave up tonight and searched these forums and found out about the CEM and the problems it can give. Is there a separate output for each headlight from the CEM and if so could I just wire the two headlights up in parallel connected to the working output or would this overload the working one.

One other odd thing is that I've always had DRL's on my volvo and I didn't even know they could be disabled. However, I noticed tonight as I was packing up that the headlights are no longer on with the switch in the "0" position. So the DRL is now disabled but this is not due to anything I've done it has done it itself. Would this indicate a problem with the CEM as well or something else.


Thanks for any advice

Russell

[Russell_S]

Ok, after a bit more research I think I am going to switch the lights with a relay that is controlled from the working CEM output.

Unless anyone else has any suggestions of course.

I'll let you know how it goes.



Russell

[coupeboy]

I've not experienced these headlight faults yet but have a nearby Volvo specialist who definitely knows how to disable the DRLs. Maybe they know about the CEM. Perhaps you have a local specialist too instead of paying Volvo dealer prices you could tap them up for assistance?

[Russell_S]

Good news, it's sorted.

In the end it wasn't the CEM at all, it was a break in the wiring between the RH headlight fuse in the engine compartment fusebox (fuse 11A/22) and the CEM connector F:13 (See attached wiring diagram). I had 12v at the fuse and about 3v at the connector and with the fuse removed and the connector disconnected from the CEM there was no continuity when checked with meter. Due to the break being buried in the wiring loom there is no chance of finding and repairing it so I have cut the offending wire in the fusebox and at the CEM connector and run a new wire along the bulkhead and into the passenger compartment to the CEM connector.

It is now working fine. I don't know how the break has managed to occur as there is no movement in the wiring loom and if there was a short circuit then you would expect the fuse to blow long before the wiring gave up.

Anyway because I originally thought it was the CEM, I took that apart and traced some of the wiring so I shall post another thread detailing what I've found out. It doesn't have solid state relays as I first thought but normal miniature PCB mounting relays. So I would think that it wouldn't be too hard to replace them if they do go faulty.

I have attached the wiring diagram detailing the headlight connections and the CEM.


Regards

Russell

[alexgriffith1983]

Thanks for the solid diagram, you wouldn't happen to have one for the taillights would you?

Alex

[Christymac]

To Russell_l

Great post with lots of inf.
I would love to be able to download your Pdf's on headlight and front beam relays but am unable to do so.
any suggestions. when I click the pdf's I just get a blank page and nothing else.
Thanks

Christy McCarthy
christymacc1@eircom.net

[baldmosher]

Unfortunately, the forum went through an attachments purge some time ago - now seems impossible to attach anything bar a single profile photo of your car and an avatar.

I've got practically unlimited storage and bandwidth on baldmosher.com, so if anyone wants to pass me any PDF attachments, I will gladly host them indefinitely (or until I actually go bald and decide baldmosher isn't such a cool name any more).

[Grumpywurzel]

I doubt if Russell will see your post Christy as he hasnt logged in since 2011 which is a loss, as like BM said the forum has had a purge and lost of things have been lost.

[Matt86]

Think I have that attachment somewhere... I'll have a look on the other laptop which is for my car bits and I'll attach if it I find it.

[Matt86]

It may help.