1.1.2 Monitoring Function

When all monitoring conditions are fulfilled, a specially defined A/F-modulation is executed. The first lean to rich cycle of the test is only used to establish an average voltage value of the downstream sensor voltage. During subsequent cycles, the calculation of the OSC is based on the accumulated value of the difference between the average value of the previous lean to rich cycle and on the measured instantaneous voltage during the current lean to rich cycle.

The relation of the deviation between the current downstream-sensor-signal and the average value of the downstream-sensor-signal is a lead for the catalyst condition.

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