Kept getting alarms on my M5 of Rear Hitch Impacts and then Bridge Encoder Timeout. I looked at the camera and saw the Arch turn too soon on drivers side hitting the rear panel of cars on the 7th cycle. It wasn't doing it every car but sporadically throughout the day. The M5 uses the ultra sonics to find the rear of the car ONLY on the 1st pass then it uses the encoder wheel and prox to count to find the back of the car throughout the rest of the wash. Since it was not hitting in the 1st cycle that ruled out it being a Ultrasonic. I changed the bridge prox and it has worked flawlessly since.