Air Injection: Description and Operation

AUXILIARY AIR PUMP
In order to ensure faster heating up of the catalytic converters of vehicles supplied to the USA and Canada, and to improve emissions when starting the engine at temperatures between 15°C (59°F) and 70°C (158°F) (engine temperature), auxiliary air is injected downstream of the exhaust valve for 1 minute after starting. The auxiliary air injection is controlled by the DME control unit that connects the appropriate relay on the relay board on the left hand side of the engine compartment to ground when the correct engine temperature is reached. The relay then closes and connects a solenoid valve and the secondary air pump to positive. Voltage is now supplied to the electric motor in the pump and the motor starts running.

The auxiliary air pump is installed underneath the hot film mass air flow sensor.