ME-SFI two-sensor control, function - GF07.61-P-3020AMG

ENGINE 156.980 in MODEL 164, 251 

ENGINE 156.982 in MODEL 209 

ENGINE 156.983 in MODEL 211, 219 

ENGINE 156.984 in MODEL 216, 221 

Fig 1: ME-SFI Two-Sensor Control Function Diagram

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

The ME engine control unit determines the lambda mean value from the signals of the O₂ sensors downstream of TWC. 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 variable (delay time) is determined for the lambda control. The correction variable (value for new O₂ sensor upstream TWC approx. 0) makes it possible to compensate for aging of the O₂ sensor upstream of TWC within certain limits. If the correction variable exceeds the limit value, the O₂ sensor upstream of TWC must be replaced.

The correction values are map-controlled and are implemented by the ME-SFI [ME] control unit by adapting the fuel injection.

Two sensor control is only enabled when the catalytic convertors have reached their operating temperature and the O₂ sensors downstream TWC operate correctly.

If limit values are exceeded, or if the plausibility check of the O₂ sensor signal is negative, a fault is stored in the fault memory and the engine diagnosis indicator lamp or for CHECK ENGINE indicator lamp lights up. The stored faults can be read out and erased with the STAR DIAGNOSIS.

The effect of the firewall catalytic converters is monitored based on the O₂ sensor signals downstream of TWC.