Emission Control Systems: Description and Operation

Secondary Air System
Function
During a cold start (+15°C to +35°C coolant temperature), the secondary air system blows air behind the exhaust valve for 65 seconds. This enriches the exhaust with oxygen, and starts after-burning, thereby reducing the catalytic converter warm-up phase. Control passes from the engine control unit 0220) across the air injector reaction pump relay 0229) to the secondary air valve (N 112, switch-over valve) and combination valve. In addition, on every subsequent start of the engine (up to a maximum engine temperature of 851C), the secondary air system will idle for 5 seconds after a delay of about 20 seconds and the self-diagnosis is run.