Left Headlight Stays on with Ignition Off

mooose · Post by **mooose** » 14 Feb 2019, 12:39

So, I turn off the ignition and the left headlight stays on. Tried rotating the light control switch, no difference. I have pulled Fuse 17 in engine compartment for now. Check all codes, nothing lamp related(I do have P0027). Any thoughts? I am suspecting CEM or maybe LSM, but how would I trouble shoot this. I do have the wiring manual.

Post by **cn90** » 14 Feb 2019, 14:06

Search forum for the mosfet/chip that controls the HL bulb.

Post by **mrbrian200** » 14 Feb 2019, 14:36

The higher wattage bulbs (forward main and high beam halogens are fed through physical relays inside the CEM. A MOSFET may provide the lower current trigger for the relay. Keep in mind it could be the relay, they can sometimes fail 'on'. Most people short of experience in electronics repair probably shouldn't try to replace relays and power transistors that are soldered to the internal circuit boards on 2005+ P2 CEMs.

mooose · Post by **mooose** » 14 Feb 2019, 14:43

Can you buy just the relay? I presume a new CEM is worth, what, $400+?
I have not been able to search " mosfet/chip that controls the HL bulb". Site says it is too busy.

Post by **mrbrian200** » 15 Feb 2019, 00:39

These relays don't plug in the side of the CEM like older P2 Volvos 2004 and earlier. From 2005+ they're internal soldered to the circuit board. A new CEM is way more than $400, most people would opt to send the one they have away to be rebuilt. There's vehicle specific programming involved so you can't just pull a CEM from a salvage yard and put it in your car. If you were to try to replace the internal relay yourself you'd need to trace the circuit within the CEM, there are no internal diagrams for these.
There are pictures of the internals here:
https://forums.swedespeed.com/showthrea ... -5t-2008my
That's from a 2008 model, however they changed little between those years, yours will look nearly if not identical on the inside. You're looking at one of the relays 1-5, 8, or 9. The two big black ones 6 and 7 are 'main relays' that are tied to things like all the interior electronics, power seats, 12v power port, CCM etc.

Unfortunately I do not know which of the little relays are tied to the main beams L or R. You'd have to trace the circuit from the connector pin B-7 back to the individual relay.

These relays can be tricky to find/order, you need to stick to exact part or identical matched specs. For example to my knowledge the two larger black relays aren't available as an exact part from Tyco (TE Connectivity) without placing special order: you have to order matched spec relays and dremel the contact spades so that they fit through the holes on the board to solder them on. Like I said most people would probably opt to send it away to have it rebuilt.

mooose · Post by **mooose** » 15 Feb 2019, 06:53

Thanks for the replies. I guess I need to take it to the dealer.

Post by **abscate** » 15 Feb 2019, 08:56

Nope - you guys have XEMODEX up in Canada who will rework your CEM For a lot less coin than the dealer

mooose · Post by **mooose** » 15 Feb 2019, 09:27

abscate wrote: ↑15 Feb 2019, 08:56 Nope - you guys have XEMODEX up in Canada who will rework your CEM For a lot less coin than the dealer

Thanks for the suggestion.

Post by **mrbrian200** » 15 Feb 2019, 10:06

The dealer may not cooperate with the idea of 'reworking' your existing CEM. The option they're likely to propose would be to install a factory new CEM at somewhere around $1000 part + labor + programming. So you're talking a range around $1500, maybe up to $2000 just to fix a malfunctioning halogen headlamp circuit. Who would have ever thought 20-30 years ago that a malfunctioning lighting control circuit might someday be considered a 'expensive car killing repair'. But that's where we seem to be with modern vehicles..

mooose · Post by **mooose** » 15 Feb 2019, 10:15

Any ideas on how to be sure it is the CEM? I hate guessing and then buy parts.