1.1.2 Monitoring Function

A specially defined A/F-modulation is executed when all monitoring conditions have been fulfilled. The test's first lean to rich cycle is only utilized in order to establish an average rear O2S voltage value. During subsequent cycles, the OSC is calculated based on the accumulated value of the difference between the previous lean to rich cycle's average value and on the current lean to rich cycle's measured instantaneous voltage.

The relation of the deviation between the rear O2S signal's current value and the rear O2S signal's average value indicates the condition of the catalyst.

A malfunction is detected in the catalyst system when the average value of the accumulated deviation exceeds a certain threshold value after a specified number of monitoring cycles have elapsed. The corresponding fault code is then stored.