Computers and Control Systems: Description and Operation

GF07.61-P-3020G ME-SFI Two-sensor Control, Function
- ENGINE 273 in MODEL 463.202 /222 /236 /237 as of model year 2009 / AEJ 08





1 Actuation of engine diagnosis indicator lamp (except code (ZU8) USA version)
2 Actuation of CHECK ENGINE indicator lamp (with code (ZU8) USA version)
A1 Instrument cluster
A1e26 CHECK ENGINE indicator lamp (with code (ZU8) USA version)
A1e58 Engine diagnosis indicator lamp (except code (ZU8) USA version)
G3/3 Left O2 sensor upstream of catalytic converter
G3/4 Right O2 sensor, upstream catalytic converter
G3/5 Left O2 sensor downstream of catalytic converter
G3/6 Right O2 sensor, downstream catalytic converter
N3/10 ME-SFI [ME] control unit
Y62y1 Cylinder 1 injector
Y62y2 Cylinder 2 injector
Y62y3 Cylinder 3 injector
Y62y4 Cylinder 4 injector
Y62y5 Cylinder 5 injector
Y62y6 Cylinder 6 injector
Y62y7 Cylinder 7 injector
Y62y8 Cylinder 8 injector
CAN C Drive train CAN

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
- LH and RH O2 sensors downstream of catalytic converter, fault-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 and the effectiveness of the firewall catalytic converters.

To do this, the ME-SFI [ME] control unit 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 [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 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 [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 [ME] control unit actuates the engine diagnosis indicator lamp via the drive train CAN or the CHECK ENGINE indicator lamp.

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