Car is possessed! What is this sensor?
 

About 1 year ago my 2008 X3 started to behave very strangely. The left blinker would not turn off, no matter what position the blinker stalk was at. It was not blinking, just on. After a restart of the car, sometimes the problem would clear, but would always come back, and sometimes it would not clear. In addition, the high beams would turn on, again with no input from the stalk.

We took to the Dealer to fix it twice (under warranty). the 1st time, they could not reproduce. We went to pick the car up, and the problem repeated immediately, so I showed the tech the issue and left.
A few days later we were told that there was an issue with the computer leveling system and the car was fixed.
So we picked it up, and the car has been fine since. Fast forward a year. Car is out of warranty and needs new brakes. We took it to a mechanic and he noticed a small black box on the front passenger lower control arm that was unpluged. He brought it to my attention, but I figured it had just come lose so we plugged it back in.
That night, I was startled when the high beams on the car suddenly turned on, and then off. The car was parked with no one in it. The left blinker than went on. This was the same issue as before.
So I disconnected the module and all is back to normal.
Does anyone know what this sensor is? It clearly measures the lower arm angle or height, but what is it for, and do I need it? I have not had it for a year, and was none the wiser. I am just wondering if its worth having fixed since I never noticed it when it was disconnected.

It is the ride height sensor: I suspect you have Xenon lights installed. Xenon projectors self adjust so if you go over bumps/imprefection they compensate for the change and avoid (to a certain degree) flashing other cars. That's why they cycle up and down when the car starts.

Good to know that's what causes the turn signal light to come on, in case it happens to me: I would have probably gone insane trying to figure this one out

Pretty stupid they unplugged it instead of replacing it...

Check your service invoice from the dealer and see what the "fix" was. I think you have a case for going back to the dealer and saying it was never fixed while under warranty and that they just unplugged it to bypass the symptoms.

Yea I would go in there and be WTF is this??? Explain how they cheated you. Now it's out of warrenty and on your dime. They couldn't figure it out... So unplug it and wait for warrenty to end. Now it's your problem.

Yes, car has xenon's. So I called the dealer, a part was replaced last year, number 61-35-3-451-624. I cannot find a diagram where the part is on the car to confirm it's the same part, but it is described as "light module". If anyone can confirm or provide a link with a diagram, I would be appreciative.

In any event, all work performed by them has a 2 year warranty, so it should be covered. Even so, the problem description is the same, so if it's not the same part, I could still make an argument that it should be covered as a pre-existing condition prior to Warranty expiration. Car goes in next week.

Giving latitude to the dealer, I will assume that the part fixed the problem, but the plug otherwise became disconnected in the past year without my knowledge. The part has subsequently failed due to dirt and water entering the unit.
The dealer said they would take care of it.

This problem took the dealer a while to diagnose, so if nothing else, I hope that anyone else with similar issues finds this helpful. Proof that these cars are very integrated!

Here's the diagram: RealOEM.com * BMW E83 X3 3.0i HEADLIGHT VERTICAL AIM CONTROL SENSOR

Aha! found it, and the part they replaced is NOT the part I am seeing on the car. Here is the picture of the part.

Item 1. This is the part that was unplugged and is subsequently failing. I cannot see the part number from this catalog.

Thanks zetatre

Interesting that the part they replaced is NOT the part I am seeing the issue with. But at least it's a cheaper part!

I've checked that parts: they replaced the whole LCM (light control module)... :yikes::wow::bustingup