One problem related to service brakes has been reported for the 1999 Audi A6. The most recently reported issues are listed below.
While driving 60 mph on the freeway, the car accelerated on its own to 72 mph as if going into cruise control. Confirmed the cruise control switch was turned off. Applied the brakes seven times. Car did not respond to braking. Engine seemed to race against the brakes. I put the car in neutral, moved to side of the road. Applied the hand brake. Turned key off. Car slowed then stopped. Since this incident the car was test driven twice by mechanics, during which it seemed to operate normally. On January 27, 2015 the car was taken to the local dealer, bellevue Audi, for diagnosis. Awaiting results.