BMW E30 ABS light on and checking the ABS sensors
E30 ABS light is on – what usually causes it?
The most common causes are the wheel sensor, its wire or connector, rust on the reluctor teeth (sensor ring), and the ABS relay and its fuse. An oxidised supply wire or a poor ground can also turn the light on. Start by measuring the sensors and checking the wiring.
How do I test an E30 ABS sensor?
Unplug the sensor connector and measure the sensor resistance with a multimeter. A good sensor reads about 1000 ohms, and all sensors should read roughly the same. A reading of zero or infinity indicates a fault in the sensor or wiring. Measure the same at the ABS unit connector to see the condition of the whole wire.
The sensors are fine but the ABS light is on or comes on only while driving. What should I check?
The reluctor teeth are often rusty or dirty, most commonly at the rear. The ring cannot be removed separately; the hub or rear axle is replaced as a whole. A loose wheel bearing can also make the pulse irregular, so check the bearing and the sensor gap.
Where is the ABS relay, and why does ABS not work even though the relay clicks?
The ABS main relay is on top of the ABS unit, and inside it is a thin fuse wire that can burn through. The relay can be faulty even if it clicks. Also check the relay's power supply and ground. The air gap of a new sensor must be about 1 mm, so check the position of the mounting tab before tightening the bolt.