VW Lupo O2 Sensor Issues, Symptoms and Solutions

I had a very similar situation with my 2001 VW Polo last year. I have some basic experience with car repairs, mostly routine maintenance and simple fixes. The check engine light came on and I noticed the same symptoms, increased fuel consumption and error codes. After checking the exhaust system, my mechanic found the oxygen sensor was functioning but there was a damaged cable connection to the sensor. The repair was straightforward, they fixed the faulty wiring and connections to the sensor for 95€. The car has been running great since then with normal fuel consumption and no warning lights. This is a common issue with these VW models from that era. Before jumping to replacing the entire oxygen sensor, it is worth having the connections and wiring checked first, as it could save significant costs. What specific error codes is your diagnostic showing? This would help narrow down whether you are dealing with the same connection issue or if there might be another problem with the exhaust sensor itself. Also, have you noticed any other symptoms like rough idling or hesitation during acceleration? These details would help determine if we are looking at the same root cause.

Service was done recently at 107000km and included new spark plugs and air filter. The error codes from the diagnostic test point to P0141 and P0135. My previous experience with oxygen sensor repairs was quite different, the catalytic converter needed cleaning before the new sensor would work properly. The check engine light initially flickered before staying on permanently. My air-fuel ratio seems off based on the black exhaust smoke. I did notice rough idling, especially when cold. Unlike your case, I checked all sensor connections and wiring, they appear intact. The fuel efficiency drop is significant, around 3L/100km more than usual. Could the sensor itself be damaged internally rather than just having connection issues? I am curious if cleaning the exhaust system components first might help resolve the issues before replacing parts. What would be the recommended troubleshooting sequence in this case?

Thanks for providing those additional details about your Lupo. Based on those error codes and symptoms, your situation does sound more severe than my initial wiring issue. The black exhaust smoke and significant drop in fuel efficiency definitely point toward a failing O2 sensor rather than just connection problems. On my Polo, when I had the rough idling fixed later, the mechanic discovered the original O2 sensor was actually degraded internally. The check engine light symptoms started similarly, with intermittent flickering before staying on permanently. The complete repair involved: Cleaning the catalytic converter, Replacing the oxygen sensor, Recalibrating the engine management system Total cost was around 380€ for parts and labor. The fuel efficiency improved dramatically after the repair, saving about 2.5L/100km. Given your error codes specifically indicate O2 sensor circuit issues, and you have already verified the connections, I would recommend replacing the sensor. The cleaning procedure for the catalytic converter can be done simultaneously since they are part of the same exhaust system.

Thanks for the thorough explanation about your Polo repair. Your experience sounds more relevant to my situation than I initially thought. Those error codes P0141 and P0135 combined with the black exhaust smoke do make a strong case for both the oxygen sensor replacement and catalytic converter cleaning. I will schedule a complete check of the exhaust system and plan for both procedures. The 380€ cost seems reasonable considering the potential fuel savings, at current prices, the 3L/100km I am wasting would offset the repair cost within a few months. The check engine light symptoms matching yours gives me more confidence this is the right path. One last question though, did your fuel efficiency improvement happen immediately after the repair, or did it take some time for the engine management system to adapt after the recalibration? I want to know what to expect after fixing these issues.