Mercedes-Benz W201 ABS warning light on
Why is the ABS light on in my W201?
The most common causes are the solder joints and fuses of the overvoltage protection relay (YJ relay) behind the battery, low charging voltage, the brake light switch, and the wheel sensor wiring or toothed ring. Go through these before replacing the ABS control unit or pump.
How do I check the wheel sensors and their wiring when the ABS light is on?
Clean the sensor tip and the toothed ring of metal dust with compressed air and check the gap between them. A loose wheel bearing can break the signal. The wiring may be broken or intermittent: the light comes on while driving, and the fault may only show when the wiring is moved.
Can weak charging turn on the ABS light in a W201?
Yes. When the charging voltage stays below 13 V, the ABS light often comes on first. Measure the voltage with the engine running. The alternator brushes or regulator may be worn. Also check the two 10 A fuses of the YJ relay, since a blown fuse turns the light on.
When is the ABS control unit the cause?
Only after the sensors, wiring, relay, fuses and charging have been checked. The fault is rarely in the control unit, but it has happened. ABS and brakes are safety-critical, so have a workshop check the result.