Secondary Air System Monitoring

General Description of Secondary Air System Monitoring

At cold start the secondary air pump and valve are switched on for their normal operating function. The secondary air delivered into the exhaust gas is causing a lean mixture indicated by the output voltage of the 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 it seems like a faulty secondary air system. Now a correction procedure follows immediately, after the secondary air system is switched off. The air/fuel 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 oxygen sensor within a predetermined time range and the correction of air/fuel influence (after secondary air pump shuts-off) is < a fixed threshold a fault will also be detected.





Monitoring Structure of Secondary Air System Monitoring