2001 VW Passat V6: Resolving P0130 and P0150 O2 Sensor Circuit Fault Codes
I initially had eight diagnostic trouble codes (DTCs), which I have since narrowed down to two primary issues: P0130 and P0150, both indicating 'O2 Sensor Circuit Malfunction'. After replacing vacuum hoses, spark plugs, the ignition module, and installing new O2 sensors, these codes persist. Notably, when I temporarily restricted the exhaust pipe using a rag, my O2 sensor readings improved significantly on the scanner—this suggests a potential leak or hole in the exhaust system. Originally, I also encountered DTCs 0491, 0492, 0300, 0301, 0306, and 0303, which have since been resolved. However, this is the first time I've seen an O2 'malfunction' code, and I initially misinterpreted it as a lean condition caused by a faulty O2 sensor. Now, I'm seeking expert advice on diagnosing and resolving P0130 and P0150 specifically in my 2001 VW Passat with a V6 engine.
Are the new O2 sensors purchased from the dealership or an aftermarket brand? These codes do not indicate a general 'O2 Malfunction' but specifically point to an 'O2 Circuit Malfunction'. Please inspect the wiring harnesses and connectors for both upstream oxygen sensors, as loose connections or damage could be the root cause.