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

GF07.61-P-3020MOS ME-SFI Two-sensor Control, Function
- as of model year 09


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 regulation active
^ Left and right O2 sensors downstream of CAT (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 control unit (N3/10) reads the following sensors:
- LH and RH O2 sensors upstream of CAT, signals from oxygen sensors upstream of CAT (catalytic converter)
- LH and RH O2 sensors downstream of CAT, signals from oxygen sensors downstream of CAT

Two-sensor control function sequence
The ME-SFI 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 new LH and RH O2 sensors upstream of the CAT is about 0) is used to compensate for aging of the O2 sensors upstream of CAT, within certain limits.

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

If the specified limit value is exceeded or if the oxygen sensor signals (upstream or downstream of CAT) fail the plausibility check, the ME-SFI control unit actuates the engine diagnosis indicator lamp on the instrument cluster (A1) (A1e58 ) over the chassis CAN (CAN E) and central CAN (CAN F).

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