Our 10 year old BMW 116i started lately to give three dash warning lights periodically, most usually after rain or driving in very wet conditions. The diagnosis is as follows: the ABS, traction control and handbrake lights come up on the dash but crucially the engine does not cut power, this indicates that it’s an issue with the front wheels as they are not the driven wheels on this model. Previously, the same symptoms had come up on the dash but the car juddered under acceleration as the traction control activated randomly. This was fixed by turning off the traction control but indicated that it was a rear ABS sensor as the ECU was not able to read the speed of the wheels and so cut power to the driven rear wheels.
Back to the job at hand, two replacement ABS sensors for the front wheels were bought. This is how to replace them:
Chock wheels, jack the car up and put on axle stands safely.
Remove the wheel
The sensor cable has two ends, one attaches to the wheel hub and counts the teeth on the wheel ring as it rotates. The other end takes this signal and connects into an electrical connector located in a plastic box in the wheel arch. This picture shows the box that houses the sensor connection.
Flip open the box with a flat headed screwdriver, there’s two tabs that need to be done. This exposes the grey connector.
It’s obvious that the built up crud is contributing to the false alarms on the dash as the crud gets wet, damp can’t escape and takes ages to dry out. So when in this far, it’s worth giving this area a good clean. I used a combination of AutoGlym Engine and Machine Cleaner, cloths, brushes and WD40. Release the grey connector and move to the wheel. Use a tort bit to unscrew the hall effect sensor at the wheel, a poor picture of which is below:
Refitting is the reverse of removal, torque up everything and take a test drive.