RS5 O2 Sensor Issues Driving Up Fuel Consumption

As someone with some hands-on experience with car repairs, I faced an identical issue with my 2017 RS4. The check engine light appeared along with increased fuel consumption, and the diagnostic scan pointed to the oxygen sensor heater element. Initially, I was also convinced the O2 sensor needed replacement. However, when I took it to the workshop, they performed thorough sensor testing and discovered the actual problem was much simpler. The air-fuel ratio readings were off because of a loose connection in the wiring harness leading to the sensor. The repair involved cleaning the connector contacts and securing the plug connection properly. Total cost was 95 Euro including diagnostic time. Since the fix, the check engine light has stayed off and fuel consumption returned to normal. Could you share some additional details about your RS5: Have you noticed any rough idling? Does the check engine light come on immediately after starting? Have you had any recent work done near the exhaust system? This information would help determine if your situation matches what I experienced or if you might be dealing with a different underlying issue.

Just had my 124672km service done last month. After checking with different workshops, I got multiple confirmations that my issue was indeed a faulty sensor in the exhaust system. The oxygen sensor was showing degraded performance in the heater circuit. A replacement sensor fixed both the check engine light and fuel consumption problems. To answer your questions: no rough idling, the check engine light would come on after about 5 minutes of driving, and no recent exhaust work. Total repair cost was 320 Euro including parts and labor. The car components are all working perfectly now and sensor testing shows optimal values across the board. If youre facing similar symptoms, I recommend getting the O2 sensor checked first before exploring other possibilities.

Great to hear you got the issue resolved. Your experience aligns with what typically happens when the oxygen sensor heater circuit fails. While in my case it was just a connection issue, a degraded sensor is actually the more common cause for these symptoms, especially at that mileage point. The malfunction indicator behavior you described, activating after 5 minutes of driving, is very characteristic of heater circuit problems, as the system needs that warm-up time to detect the fault. The repair cost of 320 Euro is also in line with what these fixes usually run. For others reading who might face similar issues: when the check engine light appears along with increased fuel consumption, having the oxygen sensor tested should be one of the first diagnostic steps. A failing O2 sensor can cause the engine management system to default to a rich fuel mixture, leading to higher fuel usage. Did you notice any improvement in throttle response after the repair? My RS4 felt more responsive once the air-fuel mixture was being properly regulated again.

Thanks for following up on my case. Yes, throttle response improved noticeably after the O2 sensor replacement. The car feels much more responsive, especially during acceleration. The workshop confirmed this was because the engine management system is now getting accurate air-fuel mixture readings from the new sensor. For anyone searching through this thread later: the combination of check engine light, increased fuel consumption, and slightly delayed malfunction indicator activation was definitely pointing to a faulty sensor. While checking connections first makes sense, in my case the sensor itself had degraded over time and needed replacement. The 320 Euro investment was worth it considering the improved performance and fuel economy. All car components are now working together properly, and regular sensor testing during maintenance should help catch any future issues before they impact performance.