The abs module in audi's 1998-2001 is a common problem. one day it was fine and the next the abs light and brake light came on the dash and went away after some driving. *tt at first the abs light would come and go. but as a week passed from the 1st day of the indecent it started to appear more often and longer. after 2 weeks the abs light and brake light stayed on.
Abs/esp light would come on after driving for 60 minutes or more, usually went off if vehicle restarted, this became more frequent over course of 10 months until light stayed on all the time, wheel sensors had to be changed at significant cost to fix problem. *tr