Thx, Tony. The sensors contact the rotor way before any service is due. I'm not suggesting that all brake noise emanates from the sensors, of course. I'm just saying that it may be the source if the squeal is coming from one of the sensored wheels. And that BMW knows that the geometry of the sensor causes noise. So, as part of the process of elimination, you may want to sand, clean and grease the sensor, as described in the linked posts, above. I bet those sensors can squeal even before contact, if they are vibrating. So, grease their side and back and their metal clips. Good luck. And happy motoring!

Psam550

 

Ha, I did a little more reading on this and it seems as the sensor makes contact ~ 50% and this seems to be where the clock start ticking or until the sensor wears enough to short out. I guess this filing and reshaping is before the last stage. I would love to read something official about exactly how the system actually works. You can read a lot of opinions out here but you just don't know how accurate it is.

 

I think I have the same problem.

And re: the above, "I would love to read something official about exactly how the system actually works. You can read a lot of opinions out here but you just don't know how accurate it is. " - I'd go a step further and say you still don't know for sure what the actual problem is until you look at your specific vehicle.

I plan to pull the left front (drivers side) wheel today and check the damn sensor, based on all I've read I think that is what is causing my squeal.

 

I can't tell you how many times going down a dirt,rocky ,or stone driveway that small pebbles have managed there way to get stuck somewhere on the brake caliper and make a nasty sound . I would go back on main road and do some hard swerves and dislodge it . I had to spray off with a hose a few times also. PIA

 

I will only add that unplugging/pulling the sensor was a little tricky. I had to pry the brake pad away from the rotor/sensor with a flathead and then grab/pull the sensor with a small vice grip carefully not to break it. Very messy in there-- dust and dirt under the finger nails and everything! Be sure to get the small metal pin/collar out, too, that secures the sensor. Clean both with a wet wipe. File it down. Apply the BMW brake grease to the side and back (dealer sells the grease in small pack for about $2.) Then reinsert. Easy to find images of the sensor and the set-up on line to help before you start. Even a video or two on how to change your brakes. Good luck! (And don't blame me if you mess it up!) Psam550.