Faulty O2 Sensor Causing Poor MPG in VW A2

I had a very similar issue with my 2006 A3 2.0 FSI last year. As someone with some experience working on cars, I initially tried diagnosing the problem myself when the malfunction indicator started acting up. The symptoms matched yours exactly, increased fuel consumption and constant check engine light. After getting the error codes related to the oxygen sensor readings, I took it to my regular workshop. The mechanic found that the wiring harness connection to the oxygen sensor was damaged, causing irregular readings and affecting vehicle emissions. The fix was straightforward, they repaired the faulty sensor connection and cleaned the plug contacts. Total cost was 95 Euro including diagnostic work. Since the repair, fuel economy returned to normal and the warning light hasnt come back. Before suggesting more specific solutions, could you share: Which engine variant does your A2 have? Are you noticing any rough idling? Has the car had any recent maintenance work near the exhaust system? This would help determine if your issue is identical to what I experienced with the wiring, or if you might be dealing with a different oxygen sensor related problem.

Just had my last service at 26000KM and getting tired of this issue. Connected my OBD reader again and definitely seeing unusual air-fuel ratio fluctuations. The faulty sensor seems to be causing unusual check engine light patterns, sometimes flashing, sometimes steady. After sensor testing multiple times, readings are inconsistent. My mechanic checked the wiring harness and connections but everything looks intact, so its likely the sensor itself thats failing. The malfunction indicator behavior matches what others described in similar cases. Might try cleaning the sensor first before replacing it completely.

Thanks for the update on your O2 sensor issues. With my 2006 A3, I initially tried cleaning the sensor too before the wiring issue was discovered, but based on your description, your case sounds different from what I experienced. The inconsistent sensor testing readings and unusual malfunction indicator behavior you describe typically point to a failing oxygen sensor rather than wiring problems. When my heater element failed, the check engine light pattern was more consistent. Since your connections are confirmed good and youve already done thorough sensor testing, cleaning might help temporarily but probably wont solve the root cause. The unusual air-fuel ratio fluctuations combined with the vehicle emissions issues suggest the sensor itself is degrading. For my A3, even after fixing the wiring, I ended up replacing the sensor at around 30000KM as preventive maintenance. The parts cost was about 180 Euro and immediately resolved similar symptoms. If cleaning doesnt improve the readings, replacing the sensor would likely eliminate both the erratic check engine light and restore proper fuel economy. The unusual nature of your issues strongly indicates sensor failure rather than a connection problem like I had.

I checked my OBD reader again today and its still showing those irregular patterns. After what youve shared about your A3 repair experience, Im starting to think cleaning might just be delaying the inevitable. The faulty sensor symptoms match exactly what youre describing, the unusual check engine light behavior and inconsistent readings during sensor testing. My fuel consumption is still higher than normal and vehicle emissions are probably affected too, so Im leaning towards just replacing the sensor completely. Since all other car components and connections have been verified as working fine, theres not much point in waiting. The 180 Euro parts cost seems reasonable considering how much extra fuel Im burning through. Will book it in next week and get the oxygen sensor replaced. Thanks for sharing your repair experience, helped confirm this is likely the same issue, just with a bad sensor instead of wiring problems.