Speed Sensor
WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 1989 Audi 90, 1989 Audi 80, 1989 Audi 200, 1989 Audi 100, and 1988 Audi 90. However, it is still accessible from the selected car via links, so may be relevant.
A speed sensor is located next to hub on each axle. A speed sensor rotor is attached to each hub and rotates past the speed sensors. The rotary motion of the wheels is picked up by each sensor and an electrical signal is sent to the ABS control unit.