Weird Xenon Levelling Issue!

[DoubleApexCa]

Hi All,

My 2002 M3 has started to have a rather odd Xenon headlight levelling issue. When I start the car, the lights go through the check process by going down, then returning to the up/straight ahead position. When I fire up the Xenon's all seems to be OK.

However, when I start driving it, over the span of say 2-3 minutes, the headlight level gradually drops until the lights are pointing down to about 15-20ft in front of the car?

My guess is that one, or both of the headlight level sensors need to be replaced. Does anyone have any other possible ideas?

Thanks in advance.
Glenn.

[Burgundy]

but the aim is good so im not motivated to fix it. There is a metal strap/bar that connects the sensor to the control arm on only one side (passnger side i think), my strap has been busted for a while and just hangs there. Check if this is the case with yours and it may be a simpler fix than replacing the whole sensor. Hope this helps.

[DoubleApexCa]

I was under the car last week as I was doing the brakes and looked at
both the front and rear sensor arms as well as the links and the
metal fittings that connect to the control arms... all appear to be
in good order.

I did have an issue late last year where the clip that attaches to
the front control arm was in fact broken. But in that case, the
symptoms were different. When the clip was broken, and the arm was
dangling loose, the headlights would not come up to level height at
all. WHen I replaced that clip, all was fine.

This time seems to be a different failure mode, wherein the lights
come up to the correct level on start, but gradually drop over time.

Thanks again
Glenn

[Eric PDX-M3]

Have you tried cycling the lights again (while driving) after the light beams drop? If the lights go back up to normal the problem may not be the sensor(s) but may be with the leveling mechanisms (stepper motors/threaded rods that adjust the angle). Although it would be odd that both have the same problem.

Have your headlight assemblies been removed or opened up lately?

Not sure what else to check. Keep us posted on what you find.

[Grimlok]

They are just potentiometers, and they can be prone to wearing out in the areas where they are used most. In this case the wear would be on one of the coil sections nearest the normal driving ride height (where the sensor is being used 99.99% of the time). I wonder if driving settles the car after a minute or two, and the lights loose their position because one of the sensors is giving a weird reading.

Before replacing them though, I am thinking there might be some schmootz in there (to use a technical term). Did you use brake cleaner or compressed air to clean anything when doing those brakes? You might have broken some dirt loose and it got inside the sensor.
By your name here, I assume you are in CA, where we have had TONS of rain lately. Might have just gotten some filth in the sensor that needs to be blown loose. Might try blasting the sensor with some air, or a spray of some brake cleaner before replacing anything.

[DoubleApexCa]

Hey Grimlok,

Well actually the Ca is for Canada, but good guess though!! I'm near Toronto, and I think I'll wait a little while yet for the temps to rise a little bit (It's been -10 Deg C. here the past week).

Thanks for the advice. I'll give that a try. I'll have a good look at those sensors and give them a good clean out. I think you may be on to something there.

One thing new I noticed is that when the I start the car up, the lights go through the self-check (down, then back up). If I let the car idle for a couple minutes, the lights seem to gradually go higher in small increments every 10 seconds or so up to a certain point. When I start driving, they start dropping. So I think your theory of the car settling while driving and the sensors giving a weird reading has merit.

Will let you all know what I find.
Thanks again.
Glenn

[Dennis]

Have you had any suspension work done recently? If the thrust arm is removed the arm on your level sensor may have kinked the other way in which case it looks ok but is sending the signal that the suspension is squatted all the way down . you can unbolt the sensor armwith a 10 mm socket and flip the arm the other way and cycle the key and drive it. its an easy check for a rather common problem.

[DoubleApexCa]

Well, finally got around to looking at this...

I replaced both the front and rear headlight level sensor modules. Lo and behold, the problem went away...

Thanks for everyone's help in diagnosing this.

Best Regards
G.