Description

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 < 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 < a fixed threshold, finally a fault will be detected.
If influence > 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 < a fixed threshold a fault will also be detected.