Two-Sensor (ME-SFI) Control Function

Task
- Improving stability of lambda control.
- Monitoring O2 sensor upstream of TWC.







The engine control module determines the lambda mean value from the signals supplied by the O2 sensor downstream of TWC. This value is compared with a stored value for optimum exhaust emissions.

If several measurements reveal that the variation is too large, a correction variable (time lag ± TV) is determined for the lambda control.

The correction variable (value in the case of new O2 sensor approx. 0) compensates within certain limits for the ageing of the O2 sensor upstream of the TWC. If the correction variable exceeds the limit value, the O2 sensor upstream of the TWC must be replaced.

In addition, allowance is made for the period of the signal supplied by the sensor upstream of TWC. If no sensor state change takes place, the lambda closed-loop control is not active and no two-sensor control is possible either in this case.


NOTE: The efficiency of the catalytic converter is also monitored by means of the signals supplied by the O2 sensor downstream of the TWC.