GF07.61-P-3020MQH ME-SFI Two-Sensor Control, Function

GF07.61-P-3020MQH ME-SFI Two-sensor Control, Function

Function requirements for two-sensor control, general points
^ Circuit 87M ON (engine control ON)
^ Engine running
^ Operating temperature of firewall catalytic converters is reached
^ Lambda control active
^ Left and right O2 sensors downstream of the catalytic converter (G3/5, G3/6) defect-free

Two-sensor control, general points
The two-sensor control is used to monitor the function of the LH and RH O2 sensors upstream of the catalytic converter (G3/3, G3/4) and the effectiveness of the firewall catalytic converter.

To do this, the ME-SFI [ME] control unit (N3/10) reads the following sensors:
- LH and RH O2 sensors upstream of catalytic converter, oxygen sensor signals
- LH and RH O2 sensors downstream of catalytic converter, oxygen sensor signals

Function sequence for two-sensor control
The ME-SFI [ME] control unit determines the lambda mean value using the signals from the oxygen sensors downstream of the catalytic converter. This value is compared with a stored value for optimum exhaust emissions.

If the deviation is too large after a number of measurements, a correction value is determined for the lambda control.

The correction value (value with a new O2 sensor upstream of the catalytic converter is about 0) is used to compensate for aging of the O2 sensor upstream of the catalytic converter, within certain limits.

If the correction value exceeds the specified limit value, the O2 sensors upstream of the catalytic converter must be replaced. The correction value depends on the performance map, and is applied by the ME-SFI [ME] control unit by adapting the injection time of the fuel injection valves (Y62).

If the specified limit value is exceeded or if the plausibility check on the oxygen sensor signals (upstream or downstream of the catalytic converter) is negative, the ME-SFI control unit actuates the CHECK ENGINE indicator lamp (A1e26) in the IC (A1) via the engine compartment-CAN (CAN C).

The exceeded limit value is stored in the fault memory by the ME-SFI control unit and can be read out and deleted using the Diagnosis Assistance System (DAS).