Audi S4 owners have reported 1 problem related to power assist brake (under the service brakes category). The most recently reported issues are listed below.
Brake booster check valve fails causing vac hose feeding to booster unit to become totally separated from valve. Result is no brake assist. This happened to me in my 2001 Audi S4!!!! at highway speed!.
See
all problems of the 2001 Audi S4
🔎.