Test Group XBMXV02.8LEV

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.

General Description - Catalyst monitoring is based on monitoring its oxygen storage capability. Engine closed loop feedback control generates lambda (air/fuel ratio) oscillations in exhaust gas. These oscillations are dampened by oxygen storage activity of catalyst. Amplitude of remaining lambda oscillations downstream of catalyst indicates storage capability.

Monitoring Procedure - In order to determine catalyst efficiency, a fixed number of complete lambda controller cycles (oxygen oscillation from upstream sensor) are used to calculate areas which are enclosed by controller curve and also calculated mean value. Average of all areas displays magnitude of oxygen admission to catalytic converter. Magnitude of oxygen admission now is used to calculate maximum permissible oscillation (areas of cycle) of downstream sensor of a still good working catalyst.

Now original measured oscillation (average of areas) from downstream sensor is compared to calculated maximum permissible value. A fault is detected if quotient (measured to calculated value) is greater than a fixed number.