Air Injection: Description and Operation

Secondary Air Injection (AIR) System

To assist in the reduction of exhaust emissions to meet European Union (EU) Stage 4 and Federal Petrol Emission standards, AIR is fitted to the vehicle.







The AIR pump is used to provide a supply of air into the exhaust manifolds during the cold start period of the engine. The AIR cycle lasts for up to 65 seconds. The hot unburnt fuel particles leaving the combustion chamber mix with the air injected into the exhaust manifolds and immediately combust.

This subsequent combustion of the unburnt and partially burnt carbon monoxide (CO) and hydrocarbon (HC) particles help to reduce the emission of these pollutants from the exhaust system. The additional heat generated in the exhaust manifold also provides rapid heating of the exhaust system catalytic converters. The additional oxygen which is delivered to the catalytic converters also generates an exothermic reaction which causes the catalytic converters to reach their optimum operating temperature and 'light off' quickly.

The catalytic converters only start to provide effective treatment of emission pollutants when they reach an operating temperature of approximately 250 degrees C (482 degrees F) and need to be between temperatures of 400 degrees C (752 degrees F) and 800 degrees C (1472 degrees F) for optimum efficiency. Consequently, the heat produced by the AIR 'afterburning' reduces the time delay before the catalysts reach an efficient operating temperature.

The AIR system comprises the following components:
- AIR pump
- AIR switching valve
- AIR control valve
- AIR vacuum reservoir
- AIR pump relay
- AIR pressure sensor (North American specification vehicles only)