Test Group YBMXV04.9S62
WARNING: This page does not describe the selected car, but rather 15 other vehicles, including the 2000 BMW Z8, 2000 BMW Z3, 2000 BMW X5, 2000 BMW M5, and 2000 BMW M Roadster. However, it is still accessible from the selected car via links, so may be relevant.
- Catalyst Monitoring General Description -
Catalyst monitoring is based on monitoring its oxygen storage capability. The engine closed loop feedback control generates lambda (air/fuel ratio) oscillations in the exhaust gas. These oscillations are dampened by the oxygen storage activity of the catalyst. The amplitude of the remaining lambda oscillations downstream of the catalyst indicates the storage capability.
In order to determine catalyst efficiency, oscillation of the upstream sensor is need to calculate "O2 in and output (catalyst)" by engine air mass and lambda deviation. The downstream sensor signal for a "threshold catalyst" then is derived (model) from this basic value. Any time the real sensor signal oscillations (downstream) correspond to the model, a defective catalyst is recognized.
- Monitoring Cycle
For catalyst monitoring structure flow chart, see Fig 1.- Computation Of Efficiency Factor - The alternating-current voltage of the oxygen sensors before and after catalyst is determined, rectified and averaged. The actual quotient ARact of the voltage of the oxygen sensor before catalyst and the voltage of the oxygen sensor after catalyst is determined. Simultaneously the theoretical quotient ARtheo of the oxygen sensors voltages are computed in dependency of the operating point of the engine. The respective operating point is determined using parameter load and engine speed. For diagnosis, the Delta (difference in change) in AR between the actual quotient ARact and the theoretical quotient ARtheo is made "Delta AR = ARact - ARtheo ". Delta AR expresses the efficiency of the catalyst. Within the time of diagnosis, an adaptation matrix is filled in dependency of the actual operating point of the engine.
- Fault Evaluation - At the end of the diagnosis period, the number of stored values in the adaptation matrix exceeding a limit is determined. If this number of stored values itself exceeds a threshold, a defective catalyst is evaluated.
- Check Of Monitoring Conditions - The monitoring principle is based on the detection of relevant oscillations of the downstream sensor signal during regular lambda control. It is necessary to check the driving conditions for exceptions where no regular lambda control is possible, e.g. trailing fuel cut-off. During such periods, and for a certain time afterwards, the computations of the amplitude values and the following processing is interrupted. Thus, a distortion of the monitoring information is avoided.