I am trying to figure out the exact same thing.
Replaced the driver side- abs/dcs/cruise control all kuput. I figured the abs sens was bad because I had to give it a pretty good whack to get it off the hub. No biggie I figure.
Drove the car for a day and determined the driver side was just as bad. Didn't have the time or energy to do it so I had my mechanic do the job. Guess what- The speedo stopped working. OK, figured both ABS senors were bad, got two new ones from bmw, put on the car and the all the problems still exist no abs/tc/speedo.
So in my mind the only thing left is that both the one I put in and the one my mechanic put in went in backwards. One side is orange and one is black, I assumed that the black side was the side with the magnet or whatever the abs sensor communicates with.