Test Group WBMXV01.9M44

WARNING: This page does not describe the selected car, but rather 14 other vehicles, including the 1998 BMW Z3, 1998 BMW M3, 1998 BMW M Roadster, 1998 BMW 750iL, and 1998 BMW 740iL. However, it is still accessible from the selected car via links, so may be relevant.

General Description - At cold start, secondary air pump and valve are switched on for their normal operating function. Secondary air delivered into exhaust gas is causing an increase of lambda sensor signal until it reaches a predetermined value. This fixed limit corresponds to minimum amount of secondary air (low-flow-limit-check). See Fig 1.

Check Conditions - To start diagnosis function, several conditions have to be satisfied: secondary air system on, no error from coolant temperature sensor, lambda sensor is heated up (stabilized condition), altitude driving conditions below 8000 feet, no error from evaporative system, no error from secondary air pump output stage, no error from battery voltage, no error from air mass sensor, no error from plausibility check of throttle valve and air mass sensor, and closed evaporative system purge valve. Furthermore, if diagnosis has already been started and one of the conditions has not been satisfied continuously, process will be interrupted.

Fig 1: Secondary Air System Monitoring

Courtesy of BMW OF NORTH AMERICA, INC.

Check Procedure

Check conditions okay.
Start monitoring procedure.
Look at signal of lambda sensor before catalyst.

If signal is below threshold for definite times: system is set and monitoring procedure is ended. If signal is above threshold for definite times: store secondary air system fault and set cycle byte. If the fault is confirmed during the next driving cycle, MIL is illuminated.