Failing O2 Sensor Boosts Scirocco Fuel Consumption

Having moderate experience with exhaust system issues, I faced a similar problem on my 2013 Golf GTI. The symptoms matched exactly what you describe, increased fuel consumption and persistent check engine light due to O2 sensor readings. Initially thought it was the sensor itself, but my workshop found it was actually just a faulty connection. The oxygen sensor wiring harness had some corrosion at the plug, affecting the air-fuel ratio readings. Total repair came to 95€, which included cleaning the connections and replacing the damaged plug. The fix significantly improved fuel efficiency and resolved the check engine light immediately. No other exhaust components needed replacement in my case. Before suggesting more specific solutions, could you share: Current mileage on your Scirocco? Any modifications to the exhaust system? Have you noticed any unusual exhaust sounds or smells? Which specific error codes showed up in the scan? This information would help determine if your issue is similar to what I experienced or if it might need a different approach to car maintenance.

Thanks for checking. Just to clarify my details: last service was completed at 74173km and all regular car maintenance is current. The scan showed error code P0135 which points to the front oxygen sensor heating circuit. No exhaust system modifications have been done and everything is stock standard. No unusual sounds, but there is a slight sulfur smell from the exhaust when idling. The catalytic converter appears to be functioning normally based on the diagnostic readouts. Would still appreciate advice on whether replacing just the oxygen sensor is enough, or if other exhaust sensor components should be checked while the repairs are being done.

Thanks for those additional details. Your Scirocco situation sounds nearly identical to what my Golf GTI went through, especially with that P0135 code. After my initial wiring fix, the problem actually returned within a few weeks. The heating circuit failure in the oxygen sensor ended up being the root cause, not just the connection issue I mentioned before. The automotive sensor eventually needed full replacement. The repair shop replaced the front oxygen sensor (320€ parts and labor) and tested the air-fuel ratio extensively to ensure the catalytic converter wasn't affected. Since your car shows similar symptoms, including that sulfur smell, focusing on the oxygen sensor replacement makes the most sense. Good news, replacing other exhaust components wasnt necessary in my case. The check engine light cleared immediately after the new sensor installation, and fuel consumption returned to normal within two tank fills. Quick tip: when the oxygen sensor was replaced, having them check the surrounding exhaust manifold gaskets was worthwhile, they often deteriorate around the same timeframe but usually just need inspection rather than replacement.

Thanks for the detailed responses. Given all the input and my P0135 code, I've decided to go ahead with replacing the front O2 sensor. The symptoms match up perfectly with what others experienced, especially the fuel efficiency issues and that sulfur smell. The 320€ estimate seems reasonable considering the diagnostic work needed. I'll have them inspect those exhaust manifold gaskets while they're working on it, but good to know I probably won't need a full exhaust system overhaul. Hoping this automotive sensor replacement will sort out both the check engine light and get my fuel consumption back to normal. Will schedule the repair next week and update once it's done. Really helpful to hear from others who've dealt with similar exhaust sensor problems, saved me from potentially replacing parts that don't need fixing yet.