The diverter valves recirculates excess boost pressure back into the turbo inlet pipe through use of vacuum actuation. The valve opens when vacuum is present, typically when the throttle is closed, to re-route the unused boost pressure. Diverter valves are a common cause of boost leaks, typically from a tear on the inner diaphragm, creating a loss of power to your engine. Replace your faulty diverter valve to restore power.