How to troubleshoot a faulty ABS sensor in an Audi 80?

My 1990 Audi 80's ABS warning light keeps coming on and off. How do I identify and fix the faulty sensor causing this issue?

First, you need to use an OBD2 scanner to check for any error codes related to the ABS system. Then, inspect all the ABS sensors, including their wiring and connections. Clean any debris or corrosion and check for any damage or wear. If the issue persists, it might be a faulty sensor and needs to be replaced.

Before replacing any sensor, check the ABS fuse and relay. If they are faulty, it can cause issues with the sensors. If the fuse and relay are fine, then you can use a multimeter to test the sensor's resistance. Compare it with the manufacturer's specifications to determine if it's faulty and replace if necessary.

I had a similar issue with my Audi 80, and it turned out to be a faulty ABS module. You can try resetting the module by disconnecting the battery for a few minutes and reconnecting it. If that doesn't work, you might need to replace the module.