500SEC (140.070) V8-5.0L (119.970) (1993)
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The ground for the sensor signal at the ME 1.0 control unit is raised to approx. +0.71 V compared to the general vehicle ground.In the event of a short
circuit of the sensor signal to ground, the ME control unit thus switches the lambda closed-loop control to open-loop mode (average value). This
prevents a high fuel consumption.
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 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.
