Originally Posted by elp_jc
Makes sense, but how the heck can it be reinstalled backwards then
? The whole purpose of this thread was to alert owners that arm could be 'reversed'. And that can't happen without removing it, no???? Just trying to make sense of all the info here.
Think about it in the context of your right leg, where your hip is the sensor: "right" is when you're sitting in a chair and your foot is on the floor. Your knee is bent in a comfortable way, and if your foot moves up and down, your hip joint pivots. Now imagine "wrong". Your your upper leg is pointed straight down, which doesn't bother your hip. To attain that position without moving your foot, your knee is bent backward 90 degrees and your calf is parallel to the floor. Now, even though your foot is the same distance from your hip as it was in the other position, your hip joint doesn't pivot if your foot moves up and down. Just like the sensor, the position doesn't damage your hip joint, but the position measuring process is disabled. As are you, unless (like your BMW) you have a very flexible ball-joint in your knee.
To respond to your "how does it get reversed?" question, the issue is that to drop the lower control arm for a suspension or spring change, you have to undo the ball joint that attaches the sensor connecting rod to the control arm you're about to drop (your "foot" in the example above). Otherwise you'll damage the sensor by ripping it's arm off. It's just a little 10mm nut to take off. When you reassemble it, the arm (your thigh) naturally hangs straight down (gravity wins!) and it's easy to pop the ball joint back into the hole and put on the nut.
That's why it's easy to re-assemble it so the sensor doesn't work.