Audi Repair: ABS, wheel speed, abs light

Question
The ABS light of my Audi A3 is always on, what could be the cause?

Answer
Uusally this means the ABS relay is bad.  There is a relay under the ABS plastic cover, which sometimes gets moisture problems.  If the ABS light does not come on until you start moving, then it could be a wheel speed sensor which is not functional.  Let me know,   Jan