Test Groups 1BMXT04.4E53 & 1BMXV04.4LEV
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2001 BMW Z8, 2001 BMW X5, 2001 BMW M5, 2001 BMW 750iL, and 2001 BMW 740iL. 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. 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. To determine catalyst efficiency, oscillation of upstream sensor is needed to calculate oxygen-in and-output (catalyst) by engine air mass and lambda-deviation. Downstream sensor signal for a threshold catalyst then is derived from this basic value. Any time real sensor signal oscillation (downstream) corresponds to model, a defective catalyst is recognized. See Figure.
- Computation of Efficiency Factor - Signal of lambda-controller is filtered and multiplied by engine air mass. A value is now added, which considers downstream sensor layer. This result is representative of oxygen load into catalyst. Standard amplitude (NSA) of downstream sensor is computed by averaging measured signals. Difference between NSA and OKB is integrated and divided continuously by a time range during which catalyst monitoring is active. This factor (GW) is an indicator of the catalyst efficiency and it is determined continuously in a certain engine speed and engine load range within time of monitoring.
- Fault Evaluation - After time range of monitoring has elapsed, efficiency factor (GW) is compared with threshold value. If GW is greater than threshold value, a fault is detected and the MIL is illuminated after next driving cycle. See Fig 1.
- Check Of Monitoring Conditions - Monitoring principle is based on the detection of relevant oscillations of downstream sensor signal during regular lambda control. It is necessary to check driving conditions for exceptions where no regular lambda control is possible (e.g. fuel cutoff). During such periods, and for a certain time afterward, computations of amplitude values and post-processing is halted, avoiding a distortion of monitoring information.