Secondary Air Injection System Description

At cold start the secondary air injection pump and valve are switched on for their normal operating function. The secondary air delivered into the exhaust gas causes a lean mixture indicated by the output voltage of the front oxygen sensor.

Any time the oxygen sensor indicates a rich mixture (voltage > a fixed limit) within a predetermined time range and the calculation of the relative secondary air mass is < (less than) a defined threshold, the secondary air injection system appears to be faulty.

A correction procedure follows immediately after the secondary air injection system is switched off. The air fuel ratio influence is determined by the deviation of the lambda-controller.

If influence < (less than) a fixed threshold, finally a fault will be detected.

If influence > (greater than) a fixed threshold the results of the diagnosis will be rejected.

As long as a lean mixture (voltage < a fixed limit) is indicated from the front oxygen sensor within a predetermined time range and the correction of air fuel ratio influence (after secondary air injection pump shuts-off) is < (less than) a fixed threshold a fault will also be detected.