S60 Electrics: CEM Diagnosis. Electrical prowess needed!

[OldFishtank]

Hello friends, first post so please go easy on me! Ill try to be as concise as possible.

My 07 S60 2.5T FWD has had the drivers-side bulb out for some time and I'm trying to work on it. This has also come with a bulb failure message.

For the life of me I cannot figure out the issue. The bulb turns on momentarily when the vehicle is started, but immediately shuts off. I've done just about everything I can think of besides ruling out the CEM. I pulled it out today to check out connectors and whatnot. I was hoping I could shoot some wires from the CEM as well to see if I'm losing continuity after the CEM.

I wanted to also shoot across the board - if possible. Ultimately my question is this: Is resistance checks from power-in (Fusebox) to power-out (B:7 [driver], B:4 [Passenger]) a valid way of ruling out an issue with the CEM? My results were noted in the attached photo along with all other useful information.

If not, what could I be doing differently? I'm not an expert in electrical but I have gotten myself this far. Any additional comments on my issue would also be helpful. Much love!

[b1mcp]

I’m not familiar with this circuit, but the readings you have presented would suggest there IS an issue with the CEM. The Left and Right resistance readings are completely different for circuits that you would expect to be the same.

Having said that, I don’t know if it’s a valid test. A better test if possible, would be to measure voltages at those points with the module plugged in and powered up.

[OldFishtank]

Thanks for the reply! I've thought about doing the same, but I'm maybe a bit worried about trying that out. In theory I'd be doing the same thing by checking voltage at the 54/23(or 22) connectors, pin 3 as they run straight from the CEM. I've already done this and similarly, on start-up the drivers side shoots up to 12v then back down.

Maybe I should check for voltage-in at B:3?

Im also a bit confused how the LSM (light switch module??) plays a part in this.

[Simmy]

iv had this problem on a v70 its the plug connections on the cem the light on each side has a relay within the cem top plugs can be acessed by removeing the wipers and scuttle cover the plugs are behind a small panel proceed carefully as pins have been known to corrode off xmodex do some good vids on cems on youtube which will show these connectors.

[OldFishtank]

Hey thanks for the reply, Simmy. I think you are suggesting that my issue is with the plug connections (b)? If so, as I've shown here, I already got the CEM out and checked both sides of the connector. No corrosion or anything visually wrong from what I can tell. Check out the pictures for yourself in OP.

[Simmy]

yes on mine at rest the left hand headlight was off and message showing on the dim headlight bulb failure with the help of an assistant to tell me if it was on or off by reaching up under the dash and pushing on the cem plug i could make the light come back on this lead me to the connection which had corrosion issues . i think your problem may lie with a dry solder joint these are common since the introduction of lead free solder . these kind of faults are common in pcb repair shops

[OldFishtank]

Originally Posted by Simmy

yes on mine at rest the left hand headlight was off and message showing on the dim headlight bulb failure with the help of an assistant to tell me if it was on or off by reaching up under the dash and pushing on the cem plug i could make the light come back on this lead me to the connection which had corrosion issues . i think your problem may lie with a dry solder joint these are common since the introduction of lead free solder . these kind of faults are common in pcb repair shops

I've already checked all wiring to the headlight (and CEM) and I've found no issues in continuity.

[Simmy]

may be the relays in the cem are failing they are replaceable but possibly a job left to an electronics specialist