Secondary Air System Monitoring

Secondary Air System Monitoring for Test Groups:

2BMXV04.4LEV: Models: 540i, 540i sport wagon
2BMXT04.4E53: X5 4.4i
2BMXT04.6XHP: X5 4.6is

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 causes 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, the secondary air system appears to be faulty. 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

Secondary Air System Monitoring for Test Group 2BMXV04.4LEV Models: 745i, 745Li

General Description of Secondary Air System Monitoring

After a cold start the secondary air pump begins and the secondary air valves open. Air is forced into the outlet ports of the engine, which mixes here with the engine gases.

Throughout the duration of the secondary air pump running the mix of the engine gases is tidily controlled. The front oxygen sensors will measure the exhaust lambda and therefore calculate the secondary airflow rate.

The measured secondary airflow rate is compared with the secondary airflow rate model and the quotient is obtained and used as the relative secondary air volume. This volume is compared with the failure secondary air threshold.

After the secondary air phase will the lambda compensation begin. During this operation condition the quality of the engine-mix-pre-control will be checked to guarantee the safety diagnostic.

When the lambda control is between pre-set limits and the relative secondary airflow rate is showed to be too low, a failure of the secondary air system is diagnosed.





Monitoring Structure of Secondary Air System Monitoring