RS7 O2 Sensor Fault Drives Up Fuel Consumption

I had a very similar issue with my 2017 RS6 last summer. Having some experience working with exhaust systems, I initially thought it was the O2 sensor too, given the symptoms you describe. Took it to my regular workshop where diagnostic testing revealed it was actually just a loose connection at the exhaust sensor plug. The increased fuel consumption and check engine light were triggered because the ECU wasnt getting proper readings from the sensor. The mechanic cleaned the connector, secured it properly, and cleared the error codes. Total cost was 95 Euro for diagnostic and repair work. Fuel efficiency returned to normal within 2 tank fills and the check engine light hasnt come back since. Sometimes the simple cable connection issues can mimic more serious sensor failures. Before jumping to conclusions about needing a new sensor, could you share: Current mileage on your RS7? Are there any other symptoms besides the fuel consumption increase? Which specific error codes is the diagnostic showing? Have you noticed any changes in engine sound or performance? This information would help determine if your issue matches what I experienced or if its potentially something different in your exhaust system.

Thanks for the insight regarding the connector issue. My current mileage is 146352 KM and last service was just 2 months ago. The air-fuel ratio has been noticeably off and I am getting P0171 and P0174 codes, suggesting a lean condition. Unlike your case, I am also experiencing slight hesitation during acceleration and occasional rough idling, especially when the engine is cold. The exhaust note sounds slightly different too, more raspy than usual. These symptoms seem to point beyond just a loose connection, possibly indicating issues with the catalytic converter or oxygen sensors affecting proper fuel mixture. Regular car maintenance schedule has been followed strictly, so this caught me by surprise.

Thanks for those additional details, especially the error codes and symptoms. Your situation does sound more complex than what I encountered with my RS6. The P0171/P0174 codes combined with rough idle and acceleration hesitation strongly suggest an air-fuel mixture issue, unlike my simple connector problem. While cleaning the oxygen sensor connections helped in my case, your symptoms point toward actual sensor degradation affecting the air-fuel ratio. After struggling with similar hesitation issues on my previous RS7, I learned that these high-performance engines are particularly sensitive to proper sensor function. The fact that your catalytic converter operation might be affected matches a common pattern where failing oxygen sensors lead to improper fuel trim. Given your strict maintenance history and the relatively recent service, I recommend focusing diagnostic efforts on the oxygen sensor system rather than just connections. When my RS7 showed these exact symptoms, replacing both upstream oxygen sensors resolved the: Check engine light, Fuel efficiency issues, Acceleration hesitation, Rough idle problems The repair cost was around 450 Euro including parts and labor, but the improvement in performance and fuel consumption made it worthwhile. Just ensure your workshop uses OEM sensors, as aftermarket alternatives caused issues for me initially.

Thanks everyone for the helpful responses. After reviewing the symptoms and comparing them with similar cases, I am now confident that my RS7 likely needs new oxygen sensors rather than just connection cleaning. Will book the car in next week and request OEM sensor replacement based on the error codes P0171/P0174 and symptoms described. The rough idle, hesitation, and altered exhaust note combined with the air-fuel ratio issues make a strong case for sensor replacement rather than just maintenance. My fuel efficiency concerns and cold start problems align perfectly with what others experienced before sensor replacement. The catalytic converter performance should improve once the engine gets proper sensor readings to maintain optimal fuel mixture. Will update once the repair is completed. Thanks again for helping me avoid the trial and error approach of testing connections first. The comprehensive diagnostic advice helped narrow down the actual issue.