The anti-lock brake system (ABS) control module may fail causing the ABS light to illuminate. Failed modules should be replaced to restore ABS operation.Google+
Car Problem Reports
Audi A6 ABS Light Due to ABS Control Module Failure
Audi A6 Problem
Visitor, 2002 Audi A6, 90,000 mi
Yellow warning light goes on at odd moments..goes off when engine is restarted but light reappears occasionally. This was checked out 4 times. Told it was a computer glitch by dealer and by other audi specialists.