VW Polo Diesel: O2 Sensor Causing MPG Drop & CEL

I had a similar issue with my VW Golf TDI from 2016, and it turned out to be exactly what you suspect. As someone with some hands-on experience working on cars, I initially tried basic sensor testing myself using an OBD reader, which pointed to the oxygen sensor. The symptoms matched perfectly, increased fuel consumption and the check engine light. After inspection at my workshop, they found a damaged wire connection to the oxygen sensor. The faulty sensor and its wiring were affecting the engine management system, causing incorrect fuel mixture readings. The repair was straightforward, took about 1.5 hours total. Cost me 95€ for the complete fix, including diagnostic work. Since then, fuel consumption returned to normal and the engine light stayed off. These car components are crucial for proper engine operation and emissions control. Before suggesting more specific advice, could you share: Current mileage on your Polo, Any other warning lights or symptoms, Whether you notice any specific driving conditions when the problem gets worse, If you have access to diagnostic codes from the check engine light This information would help determine if your issue is identical to what I experienced with the sensor wiring.

Thanks for the helpful details. Just had my service done last week at 14373km. After reading your experience, I am more confident it points to the oxygen sensor. I did notice the fuel consumption issue gets worse during cold starts, which seems to match the heater element theory. The exhaust system seems fine otherwise, and there are no other warning lights besides the check engine light. The diagnostic scan shows P0135 code related to the oxygen sensor circuit. Think I will follow your advice and have the sensor replaced, especially since the repair cost and time seems reasonable. The timing actually works well since I need to maintain proper emissions for the upcoming inspection period.

Glad you got the diagnostic code, P0135 definitely confirms what we discussed about the oxygen sensor heater element. The cold start symptoms you mentioned are a classic sign, as the heater element is specifically designed to bring the sensor up to operating temperature quickly. On my Golf, I noticed the exact same pattern with cold starts before getting the repair done. The faulty sensor caused the check engine light to appear more frequently during colder weather. Worth mentioning that after my repair, I saw about a 15% improvement in fuel consumption. Since your mileage is relatively low at 14373km, this might be covered under warranty, worth checking with your dealer. My repair was just outside the warranty period, which is why I paid the 95€. The fact that your exhaust system shows no other issues is good news. A properly functioning oxygen sensor is crucial for both optimal fuel efficiency and emissions control. With the P0135 code and the symptoms matching, you can be confident about proceeding with the repair.

The diagnostic code P0135 and your experience match my situation perfectly. The cold start symptoms really helped confirm my suspicions about the oxygen sensor heater element being the root cause. The air-fuel ratio issues during cold weather definitely explain the increased fuel consumption I have been seeing. Knowing the repair only takes about 1.5 hours and costs around 95€ makes me feel better about scheduling the work. I will contact my dealer first though, since with only 14373km on the odometer, this might still be under warranty coverage. Good to hear your fuel consumption improved significantly after the fix. I am looking forward to getting the exhaust system back to optimal performance, especially with the inspection coming up. Having a properly functioning oxygen sensor will ensure both better efficiency and correct vehicle emissions. Thanks for sharing your experience, it helped me understand the issue and make an informed decision about the repair. Will schedule the sensor replacement this week to avoid any long-term engine health issues.