Last week my E46 323i started idling rough and after checking fault codes on BMW Scanner and Torque, I determined one of the O2 sensors had failed. Changed both sensors but the fault persisted. Dug a little deeper and discovered that Pre-cat O2 sensor #2 has a constant voltage output of 0.4V however #1 varies continuously between 0.1V and 0.8V.
Figuring one of the new sensors was bad, I swapped the leads around just to be sure however #2 still showed as bad. i.e. the fault stayed with #2 regardless of which sensor was plugged in.
Now I am stuck as I don't know quite where to look next. What could be causing the circuitry to detect 0.4V continuously. I believe this may be the default voltage if the cabling is open circuit but since the wires seem to run straight to the ECU and the sensor cable grounds are properly grounded I am unsure where to look.
Any ideas welcome as I have wasted all day getting precisely nowhere with this.
Figuring one of the new sensors was bad, I swapped the leads around just to be sure however #2 still showed as bad. i.e. the fault stayed with #2 regardless of which sensor was plugged in.
Now I am stuck as I don't know quite where to look next. What could be causing the circuitry to detect 0.4V continuously. I believe this may be the default voltage if the cabling is open circuit but since the wires seem to run straight to the ECU and the sensor cable grounds are properly grounded I am unsure where to look.
Any ideas welcome as I have wasted all day getting precisely nowhere with this.
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