Left Low Beam Headlight Issue

jmattchew · Post by **jmattchew** » 03 Feb 2016, 20:36

Hey all so I really hope someone here has an idea about this because I'm stumped!

So, my left and right low beam headlights both burnt out a few months ago, around October, they turned pink and slowly got worse and worse until they died (so I knew it was the bulbs, not an electrical issue), and then I replaced them, and they worked great until recently! About a month ago or maybe a little more, my left low beam headlight would just go out randomly. Usually it was after I started the car and started driving for a little bit, like a minute or so. Now it goes out almost as soon as I start the engine. But usually when the car starts it is on, bright blue (not pink) for a few seconds and then goes out.

I first assumed that the bulb couldnt be dead, because the bulb was recently replaced and it didn't even start fading or anything. So I decided it must be electrical. I opened up the headlight thing and everything looked fine, although, (and i don't know if this is relevant) but it smelled pretty bad in there, I'm not sure why.

I assumed it was just a strange electrical issue and right now I can't afford to fix it so I've just left it. The right low beam works great, the two high beams work great as well. and the driving lights do too. But here's the kicker- yesterday driving home from work, when i started the car, the bulb was on and worked. The entier 20 minute drive home, the left low beam worked!! I was so confused. This morning however, when I started the car, it was dead again.

Do you guys have any ideas??

bob-in-va · Post by **bob-in-va** » 18 Feb 2017, 13:41

Hi,

I purchased a 2007 S40 a few months ago and have the same issue, driver's side low beam comes and goes. These are standard bulbs, not the Bi-Xenon. I swapped bulbs L/R and problem stayed on the driver's side. I have no history since the car is new to me; but no flicker, no weird smells, no pink glow, all connectors and wires look fine. It is either on or off, and the dash INFO indicates a low beam bulb failure. The wiring diagram shows the low beam connections going straight into the CEM on E25 and E37, with a symbol on the CEM outline that looks like a Field Effect Transistor (FET). Since bulbs are high current, I assume they must be switched through a solid state device internal to the CEM.

I hope I am wrong, but it appears to me like the CEM must be cracked open to either service/replace the device or the CEM is sending the wrong control to the switching device. Can any one else shed some light (no pun intended).

Bob-in-va

mf70 · Post by **mf70** » 13 Mar 2017, 09:21

I haven't had to go in myself, but AFIK the headlights are powered through relays on the CEM board. I suspect the FET activates the relay. The circuit board is relatively open.

Others have reported success with either refreshing the soldering to the relays or replacing them. They are a standard electronic part.

bob-in-va · Post by **bob-in-va** » 17 Mar 2017, 17:30

Thanks. That's where I thought this was going, but I think I have dodged the bullet. This has been a very intermittent problem and started working for a long stretch but finally started dropping out again. I observed the harness connectors to the headlight assemblies are the same. Since these assemblies come out so easily, I swapped them when I was able to catch it in the act. Behold, the problem moved to the passenger side! Closer inspection of the connector leaf to the halogen bulb revealed it had lost a lot of the spring tension on the hot wire. I was able to tease it back into shape with a dental pick, put some bulb grease on it, and it has not misbehaved for a solid week. This was a surprise to me because weak connectors with that kind of current typically arc and flicker until the connector burns up. In this case. the computer must sense the current and prevent any arcing. That is simply crazy to put relays inside the CEM; glad I have not had to take that journey. I once had a Cherokee that had a bad clutch cylinder. Usually no problem, but this jewel was not even replaceable, the cylinder sleeve was cast into the INNER wall of the bell housing AARRRG!!!! Had to pull the engine to replace a few rubber cups. Why do they do stuff like that. Anyway, thanks for the response.

-Bob