Many Audi's have exhaust systems with bypass valves. Also known as valved exhaust systems, sport exhaust system, dual-mode exhaust systems, etc. I don't believe there is any standard nomenclature.

When auto companies started including these exhaust systems with bypass valves, the actuators were vacuum operated. The ECU then controlled a vacuum solenoid valve which in turn opened and closed a butterfly valve that would provide two paths for the exhaust gases. One path diverts the gas flow into the muffler and the other path diverts the gas flow to bypass or partially bypass the muffler.

Recently, Audi (and some other manufacturers) have changed the actuator style from vacuum operated butterfly valves to electric servo-motor butterfly valves. I was looking at a new S6 today and noticed that the butterfly valves were controlled by an electric servo-motor.

  • Does anyone know when the transition from vacuum control to servo-motor control occurred?
  • Has anyone with electric servo-motor controlled valves disconnected the plug at the muffler? What was the result?
  • On the servo motor controlled valves, it appears that the default state is valve open. Can anyone describe the change in state that occurs after starting engine? I assume after initial start, the bypass valves close. When do the valves open? Do the valves fully open or partially open?


I would appreciate anyone with knowledge on the electric servo motor valves to help me understand the operation.

Thanks,

Steve