Test Group XBMXV04.4LEV & XBMXV05.4LEV
WARNING: This page does not describe the selected car, but rather 14 other vehicles, including the 1999 BMW Z3, 1999 BMW M3, 1999 BMW M Roadster, 1999 BMW M Coupe, and 1999 BMW 750iL. However, it is still accessible from the selected car via links, so may be relevant.
Secondary Air System Monitoring 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 a lean mixture indicated by output voltage of oxygen sensor. Any time oxygen sensor indicates a lean mixture within the maximum time for monitoring, a counter is incriminated by "one" up to a predetermined value. This fixed limit corresponds to the minimum amount of secondary air (low-flow-limit-check). For secondary air system monitoring flow chart, see Fig 1.