2003 3BMXV06.0N73
Secondary Air System Monitoring General Description - After a cold start, secondary air pump begins and secondary air valves open. Air is forced into outlet ports of engine, which mixes with engine gases. Throughout duration of secondary air pump running, mix of engine gases is controlled. Front oxygen sensors will measure exhaust lambda and therefore calculate secondary airflow rate. Measured secondary airflow rate is compared with secondary airflow rate model and quotient is obtained and used as relative secondary air volume. Volume is compared with failure secondary air threshold. After secondary air phase, lambda compensation will begin. During this operation condition, quality of engine/mixture/pre-control will be checked to guarantee safety diagnostic. When lambda control is between preset limits and relative secondary airflow rate is showed to be too low, a failure of secondary air system is diagnosed. See Fig 1.