BMW E38 ABS and traction control light on
Why are the ABS and traction control lights on in an E38?
The most common causes are a fault in a wheel sensor or its wiring, a broken internal wire or bad solder joint in the ABS unit, the pre-charge pump, and connectors loosened by moisture or vibration. Tyres of different sizes front and rear can also turn the lights on. Read the fault codes first, because sensors do not usually fail on their own.
How do you confirm a wheel sensor or wiring fault?
An 'open circuit' code means a break in the sensor's wire or connection, not usually in the tone ring. Measure the sensor and the wiring with a multimeter from the ABS unit connector. With a diagnostic tool you can see each wheel's speed data while driving. A light that comes on as soon as the power is on points to the unit's power supply; one that comes on only while driving points to a sensor.
Why does the speedometer stop working along with the ABS light?
The speed signal comes from the ABS sensors, so a dead sensor or a broken sensor wire also stops the speedometer. Sometimes the wiring harness running under the rear seat has melted because of a short circuit in the reversing light. A sign can be a dimly lit reversing light. Wiring is repaired by soldering and heat-shrink tubing.
Why does the traction control light (ASC or DSC) come on after a new ABS unit or steering wheel sensor?
DSC is a driving stability system in which a separate sensor reads the steering wheel angle. If the sensor is broken or uncalibrated, the system switches itself off. A replaced ABS/DSC unit must be coded to the car and calibrated. Leave this to a workshop.