1 | Fault code | on right upstream of TWC on right downstream of TWC (only for and EURO3/4, not for Model 463) on right upstream of TWC on left upstream of TWC on left downstream of TWC (only for and EURO3/4, not for Model 463) on left upstream of TWC |
2 | Fault storage Activation of malfunction indicator lamp for engine diagnosis (EURO3/4) or CHECK ENGINE (MIL) | after the end of the test period and faults after two successive driving cycles with faults |
3 | Frequency of the test | continuous |
4 | Checked signal or status | A. Limits for oxygen sensor signal B. Sensor status change |
5 | Fault setting conditions A. Limits for oxygen sensor signal Lower limit Upper limit Test duration B. Sensor status change |
Voltage must not be less than -0.15 V Voltage must not be greater than 1.5 V approx. 5 s After approx. 220 s with sensor heating switched on, the sensor signal must not dwell in the voltage window 0.4 - 0.6 V for longer than approx. 15 s. |
6 | Test prerequisites | - engine speed approx. 1000 - 2000 rpm - load approx. 15 - 50 % - three-way catalytic converter temperature > 380 °C - lambda control enabled |
7 | | The following electrical connection faults of the oxygen sensors upstream and downstream of TWC are detected by the tests: line interruption, short circuit and shunt (high-resistance short circuit) to ground or battery voltage. Line for oxygen sensor signal has shunt or limited voltage increase in oxygen sensor signal Interruption of oxygen sensor signal ground. With cold oxygen sensor, shunt to +12V or ground of ME-SFI control module. With short circuit of oxygen sensor ground to +12 V, the ME-SFI control module is destroyed! |
P07.61-2531-11
Sensor back voltage, shown on Engine 137
G3/11 Left oxygen sensor downstream of TWC, cylinders 7 - 9
x1 Connector
1 Sensor heating terminal 87
2 Sensor heating ground
3 Sensor signal ground
4 Sensor signal (approx. 0.45 V at λ = 1 and oxygen sensor at operating temperature)
N3/10 ME-SFI control module
4x Amplifier for sensor signal analysis circuit and sensor signal ground
0.268 V Back voltage with respect to ground (term. 31)
Z6/4 Connector sleeve for sensor signal ground (4 oxygen sensors, M137 only)
Z7/36 Terminal 87 connector sleeve
The ground for the sensor signal is increased at the ME-SFI control module to approx. +0.268 V compared to the general vehicle ground. The analysis circuit for the oxygen sensor signal outputs this "sensor back voltage" of approx. 0.268 V. If the oxygen sensor is cold, the sensor internal resistance (Nernst cell) must be high enough, irrespective of the mixture composition, for the oxygen sensor voltage to be initially the same as the back voltage.
By testing the back voltage, line interruption, short circuit and shunt (high-resistance short circuit) to ground or battery voltage will be detected.
With a short circuit of the sensor signal to ground, the ME-SFI control module switches the lambda control to open-loop operation (mean λ value). This prevents a high fuel consumption.