Mercedes-Benz W126 ABS light and wheel sensors
The W126 ABS light is on, what can cause it?
The most common cause is a break in the wheel sensor wire, often in the sensor's or the rear wire. The light may come on only at a certain speed or, for example, after work on the wheel. The same wheel speed sensors serve both ABS and ASR. Brakes are safety-critical, so have a workshop check the result.
How are the wheel sensor and its wire checked?
Measure the sensor's resistance with an ohmmeter; the guideline is about 1000 ohms. Check the wire with a resistance measurement while wiggling it during the measurement, which reveals a break. An old sensor can be hard to get as a spare part, and the sensors are awkward to reach.
How is the front wheel ABS sensor removed when it is stuck?
When the mounting bolt is out but the sensor will not come off, it can be heated and tapped with a socket from the other side. Also check whether the sensor's O-ring is holding it. When installing, clean the rust from the hole and use copper paste as lubricant. After brake work, have a workshop check the result.
How are W126 ABS faults read?
The ABS control unit has a diagnostic connector from which fault codes are read. Reading requires a tool, which you can get from a workshop. Reading the codes tells which sensor or wire is faulty before parts are replaced.