Mercedes-Benz W211 ABS sensor and wheel speed signal
Why do the W211's ABS and ESP lights come on because of an ABS sensor fault?
The lights come on when the car receives an incomplete or implausible speed signal from a wheel. The cause is the sensor or the magnetic ring it reads. At the front, a torn brake dust shield can rub on the ring or rise on top of it.
How does the distance between the sensor and the magnetic ring matter?
The distance between the sensor and the ring must be correct. If the hub has been fitted too deep, for example after a bearing replacement, the sensor gets no contact from the ring. Clean the sensor's mounting location so that the sensor sits at the correct distance.
The ABS light is on although the sensor and ring have been replaced. What could be the cause?
The new or old ring may already be broken or may break during installation. The ABS checks the wheel signals only when the speed exceeds 20 or 40 km/h, so the light comes on only then. Check the ring's condition and installation.
Can you repair an ABS fault yourself?
ABS and ESP are safety devices of the braking system, so replacing the sensor or ring must be done carefully. Have a workshop check the result and read the fault codes. Do not ignore the warning light.