L6/1 Left front wheel speed sensor L6/2 Right front wheel speed sensor ABS only L6 Rear axle speed sensor ETS, ASR, ESP only L6/3 Left rear wheel speed sensor L6/4 Right rear wheel speed sensor       P42.30-0221-06   Wheel speed sensor, location The front wheelspeed sensors (L6/1 and L6/2) are mounted on the front steering knuckle assemblies. ABS: The rear wheelspeed sensor (L6) is located on the differential assembly. ETS, ASR, ESP: The rear wheelspeed sensors (L6/3 and L6/4) are mounted on the rear wheel carriers.     Wheel speed sensor, task To supply the current wheel speed to the ABS, ETS, ASR or ESP control module (N47-7, N47-2, N47-1 or N47-5).     Wheel speed sensor, design Inductive sensor: Coil with magnetic core installed at a defined distance from reluctor on the front wheel hub, the rear halfshafts or the drive pinion at the rear axle.     Wheel speed sensor, function The magnetic field of the wheel speed sensor is intersected by the teeth of a rotor. This changes the magnetic field and the coil induces an AC voltage. The frequency of this alternating current, governed by the number of teeth on the reluctor, fluctuates to reflect variations in wheelspeed, is proportional to wheelspeed.