How to troubleshoot ABS brake failure in an Audi 80?

My Audi 80's ABS brakes seem to have failed suddenly while driving on the highway. The ABS light is not on and I can still brake, but it feels like the ABS system is not working. What could be the cause of this sudden failure and how can I troubleshoot it?

First, check the sensors and wiring for any damage or loose connections. These are common causes of ABS brake failure. If everything looks fine, try resetting the ABS system by disconnecting the battery for a few minutes before reconnecting it.