i have an 2000 audi a6 quattro and my ABS light did the same as yours but my braking was just fine as always. I was going to take it to a dealer when my Brother-in-law who's a mechanic said that audi did a bad job insulating ABS sensors and they get dirty and "gunky" after a while. if you clean it your light should go away, if not then you got some diagnostic work and some change to cough up.