C 320 Wagon (203.264) V6-3.2L (112.946) (2004)
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ME 2.0, ME 2.1, ME 2.7, ME 2.8 with engine control unit for EURO 3/4
The ground cable for the sensor signal for each O2 sensor is routed up to the ME control unit.
The ground for the sensor signal is increased to approx. +0.268 V compared to the general vehicle ground e.g. at the ME 2.1 control unit. In the event of
a short circuit of the sensor signal to ground, the ME control unit thus switches the lambda control to open-loop mode (average lambda value). This
prevents a high fuel consumption.
The analysis circuit for the O2 sensor signal outputs a so-called sensor back voltage of approx. 0.470 V. If the O2 sensor is cold, the sensor internal
resistance is so high that the O2 sensor voltage is initially equal to the backvoltage irrespective of the mixture composition.
The backvoltage at the ME control unit can be measured to the sensor ground if the O2 sensor is disconnected.
ME-SFI Lambda Control Function
ME-SFI Lambda Control Function
Shown on Engine 119
158
Three-way catalytic converter
B2/5
Hot film mass air flow sensor
B11/4
Coolant temperature sensor
B37
Accelerator pedal sensor
G3/3
Left O2 sensor upstream of TWC
G3/4
Right O2 sensor, upstream of TWC
N3/10
ME-SFI control unit
Y62
Injectors (LH-SFI, HFM-SFI, PEC [LH, HFM, PMS])
The mixture composition is maintained within the narrowest possible limits around lambda = 1 in order to achieve a high conversion of the exhaust
gases in the catalytic converter.
The O2 sensor reacts to the oxygen concentration in the exhaust and transmits the corresponding voltage signal to the ME-SFI control unit for fuel
injection, which thereupon alters the mixture composition in such a way as to produce a mixture composition of lambda = 1 in all operating states when
the lambda closed-loop control is active. This procedure is constantly repeated (control loop), the frequency is dependent on engine load and speed. The
ME-SFI control unit alters the mixture composition with a time delay in order to prevent any risk of jerking. The lambda closed-loop control is
operational in the following conditions (closed-loop control):
