Adaptive Xenon Headlight intermittent vertical calibration problem

[pablom2c]

Hi,

Four months ago I bought a used 2008 135i with 30,000km/19,000 miles.

Lately I have noticed that when I start the car and the headlights do their calibration dance, the right headlight appears to get stuck sometimes and not do the complete dance (only moving down, and not coming up again). Sometimes the right headlight points down to the ground in front of the car instead of straight. Other times I start the car and the right headlight does the calibration correctly and points perfectly straight like it should.

So the problem with the right headlight is intermittent, sometimes it points straight correctly and sometimes it points down, I can’t find any reason or cause to when or why it works or not. Also the right headlight doesn't seem to be loose, it doesn't wobble either when it ends up pointing down or straight. The left headlight always does the calibration correctly and always points perfectly straight, so there’s no problem with the left headlight.

Also when I move my steering wheel left and right (adaptive lights) both headlights work perfectly following the road, even when the right headlight ends up pointing down to the ground after calibration. I always use the headlights on the automatic position.

Is this a vertical aim sensor problem? Or is it a problem with my right headlight motor/or something else? The car doesn’t report any faults, and the light on the light switch is always green (it doesn’t flash).

My mechanic checked the vertical aim sensor but only found the one on the front axle near the left wheel and said it was fine. But I’ve also read there’s another sensor in the back axle but he couldn’t find it? Why are there 2 sensors? Is there one for each headlight or how does it work? What could be causing my problem?

Is it just a sensor or is it the headlight?

Thanks a lot for your help.

[awns729]

Grab the headlight with your hands and see if you can move or shake it. I know you said it does't seem to be lose or wobble, but I just want to make sure you've physically tried to shake it and you don't just mean that it doesn't shake while you're driving. If you can move the headlight with your hands, likely all 4 brackets are broken. If that's the case, I have a thread on all the info you need. It'll take $25 bucks and a few hours to repair. If that's not the case, then I have no damn idea and hopefully someone else can chime in.

Also, I think the front and rear sensors (don't quote me) combine to figure out how the front + rear suspension is loaded relative to the road. If the rear is more compressed than the front, the front is higher, so to keep a level beam, the car should point the lights down to kind of counter-balance (stated differently, if an 800 lb gorilla sat on your car's ass, your BMW would keep the headlights perfectly level... gotta love German engineering ). If the front sensor says the front suspension is more compressed than the rear (like during heavy braking), it'll point the lights up a little bit to, once again, keep that level beam. You can almost notice this happen during hard braking. So AFAIK that's the purpose of 2 sensors.

[pablom2c]

Thanks for your comment. The headlight is not loose, it is completely attached and no tabs are broken.

If one or both sensors were faulty the left headlight that always works correctly would not level right? So if only one headlight (right) doesn't calibrate properly then it must be the headlight itself? Can anyone confirm? Thanks.

[pablom2c]

Can anyone help me with my last question? Thanks.

[awns729]

While I don't really know, your logic certainly seems sound. I would imagine bad sensor readings to affect both headlight's calibration dance like you're saying, not just one. Is swapping the motors from one headlight to another something that you can easily try? I believe servos have a reading sent back to the computer that's supposed to indicate what position they're at as they're moving. Maybe something is wrong with the right one. Just a thought, but I hope someone with more experience chimes in. You can also try the 3 series forum - headlight design is likely the same but they have more viewers. Good luck.

[Horigan]

I've had the internal motor become disconnected from the headlight on my 335i. I had to pull front wheel well liner and headlight rear cover off to find the links and snap them back in to place. My issue was a complete disconnect, but maybe your issue is a partial disconnect. There's a small white plastic ball that snaps in to a receiver. With the back cover off I was able to move the mechanism and figure out which direction was disconnected.

Good luck.

Rich

[pablom2c]

Thanks for your last comments, I will try opening the headlight and check if it is partially disconnected since it doesn't appear to be the sensors.