S5 O2 Sensor Issues, Rich Running and Fuel Problems

I had a very similar issue with my 2014 Audi S4 last year. Having some experience with basic car maintenance, I initially tried scanning the error codes myself. The symptoms you describe match exactly what I experienced, high fuel consumption and the engine running rich. After seeing the O2 sensor readings, I took it to my regular workshop for a proper diagnosis. Turned out the O2 sensor connection was loose, with some corrosion on the plug. The air-fuel ratio was all over the place because of this faulty connection. The fix was straightforward, they cleaned the connections and secured the wiring properly. Total cost was 95 Euro including diagnostic work. No need to replace the actual sensor or check the catalytic converter in my case. Before suggesting specific solutions though, could you share: Have you noticed any unusual exhaust smell? When was your last routine car maintenance? What specific error codes are you getting? Is the check engine light steady or flashing? This info would help determine if your issue is similar to what I encountered or if there might be other factors to consider.

I had a very similar issue with my 2014 Audi S4 last year. Having some experience with basic car maintenance, I initially tried scanning the error codes myself. The symptoms you describe match exactly what I experienced, high fuel consumption and the engine running rich. After seeing the O2 sensor readings, I took it to my regular workshop for a proper diagnosis. Turned out the O2 sensor connection was loose, with some corrosion on the plug. The air-fuel ratio was all over the place because of this faulty connection. The fix was straightforward, they cleaned the connections and secured the wiring properly. Total cost was 95 Euro including diagnostic work. No need to replace the actual sensor or check the catalytic converter in my case. Before suggesting specific solutions though, could you share: Have you noticed any unusual exhaust smell? When was your last routine car maintenance? What specific error codes are you getting? Is the check engine light steady or flashing? This info would help determine if your issue is similar to what I encountered or if there might be other factors to consider.

I had a very similar issue with my 2014 Audi S4 last year. Having some experience with basic car maintenance, I initially tried scanning the error codes myself. The symptoms you describe match exactly what I experienced, high fuel consumption and the engine running rich. After seeing the O2 sensor readings, I took it to my regular workshop for a proper diagnosis. Turned out the O2 sensor connection was loose, with some corrosion on the plug. The air-fuel ratio was all over the place because of this faulty connection. The fix was straightforward, they cleaned the connections and secured the wiring properly. Total cost was 95 Euro including diagnostic work. No need to replace the actual sensor or check the catalytic converter in my case. Before suggesting specific solutions though, could you share: Have you noticed any unusual exhaust smell? When was your last routine car maintenance? What specific error codes are you getting? Is the check engine light steady or flashing? This info would help determine if your issue is similar to what I encountered or if there might be other factors to consider.

Thanks for the detailed response. My last service was about 6000km ago where they did a standard maintenance check. I do notice a slightly stronger exhaust smell lately, especially when idling. The check engine light stays steady, not flashing. The error code reader shows P0172 which points to a rich fuel mixture condition. Looking at my car maintenance history, the oxygen sensor has never been replaced in these 84277km. From what I understand, failed O2 sensors commonly cause poor fuel efficiency and the exact symptoms I am seeing. Based on your experience with sensor connections, I will get that checked first before replacing parts.

Thanks for the detailed response. My last service was about 6000km ago where they did a standard maintenance check. I do notice a slightly stronger exhaust smell lately, especially when idling. The check engine light stays steady, not flashing. The error code reader shows P0172 which points to a rich fuel mixture condition. Looking at my car maintenance history, the oxygen sensor has never been replaced in these 84277km. From what I understand, failed O2 sensors commonly cause poor fuel efficiency and the exact symptoms I am seeing. Based on your experience with sensor connections, I will get that checked first before replacing parts.

Thanks for the detailed response. My last service was about 6000km ago where they did a standard maintenance check. I do notice a slightly stronger exhaust smell lately, especially when idling. The check engine light stays steady, not flashing. The error code reader shows P0172 which points to a rich fuel mixture condition. Looking at my car maintenance history, the oxygen sensor has never been replaced in these 84277km. From what I understand, failed O2 sensors commonly cause poor fuel efficiency and the exact symptoms I am seeing. Based on your experience with sensor connections, I will get that checked first before replacing parts.

Good to hear back from you. Since you mention the P0172 code and steady check engine light, this does sound quite different from my connector issue. The stronger exhaust smell combined with the rich fuel mixture reading really points toward a failing oxygen sensor in your case, especially given the mileage. On my S4, I initially thought I needed a full sensor replacement too, but got lucky with just the connection issue. However, the air-fuel ratio usually stays fairly consistent with just connection problems. Your symptoms suggest the sensor itself is actually degrading and affecting mixture calculations. Since your automotive sensor has never been replaced in 84277km, replacing it would be a smart preventive car maintenance move anyway. These sensors typically last 60000-80000km. When mine eventually failed last month, I finally did need a full replacement, which cost around 280 Euro including labor. Just make sure they check the entire exhaust sensor wiring while doing the replacement. In some cases, heat damage near the exhaust manifold can affect the new sensor if not addressed. Let us know how it works out, did you schedule the repair yet?

Good to hear back from you. Since you mention the P0172 code and steady check engine light, this does sound quite different from my connector issue. The stronger exhaust smell combined with the rich fuel mixture reading really points toward a failing oxygen sensor in your case, especially given the mileage. On my S4, I initially thought I needed a full sensor replacement too, but got lucky with just the connection issue. However, the air-fuel ratio usually stays fairly consistent with just connection problems. Your symptoms suggest the sensor itself is actually degrading and affecting mixture calculations. Since your automotive sensor has never been replaced in 84277km, replacing it would be a smart preventive car maintenance move anyway. These sensors typically last 60000-80000km. When mine eventually failed last month, I finally did need a full replacement, which cost around 280 Euro including labor. Just make sure they check the entire exhaust sensor wiring while doing the replacement. In some cases, heat damage near the exhaust manifold can affect the new sensor if not addressed. Let us know how it works out, did you schedule the repair yet?

Good to hear back from you. Since you mention the P0172 code and steady check engine light, this does sound quite different from my connector issue. The stronger exhaust smell combined with the rich fuel mixture reading really points toward a failing oxygen sensor in your case, especially given the mileage. On my S4, I initially thought I needed a full sensor replacement too, but got lucky with just the connection issue. However, the air-fuel ratio usually stays fairly consistent with just connection problems. Your symptoms suggest the sensor itself is actually degrading and affecting mixture calculations. Since your automotive sensor has never been replaced in 84277km, replacing it would be a smart preventive car maintenance move anyway. These sensors typically last 60000-80000km. When mine eventually failed last month, I finally did need a full replacement, which cost around 280 Euro including labor. Just make sure they check the entire exhaust sensor wiring while doing the replacement. In some cases, heat damage near the exhaust manifold can affect the new sensor if not addressed. Let us know how it works out, did you schedule the repair yet?

Based on the helpful information and confirmation about exhaust sensor issues, I decided to book an appointment at a repair shop for next week. The steady check engine light and P0172 code, combined with my car never having the O2 sensor replaced in 84277km, make sensor replacement seem like the logical fix. The stronger fuel smell and poor fuel efficiency match what others experienced with failing sensors. Even if the wiring check shows no issues, replacing the sensor makes sense given its age and impact on the air-fuel ratio. At around 280 Euro for parts and labor, this seems like a reasonable investment to restore proper engine function. I will update once the repair is complete. Thanks for sharing your experience, it helped confirm my suspicions about the sensor being the root cause rather than just connection issues.

Based on the helpful information and confirmation about exhaust sensor issues, I decided to book an appointment at a repair shop for next week. The steady check engine light and P0172 code, combined with my car never having the O2 sensor replaced in 84277km, make sensor replacement seem like the logical fix. The stronger fuel smell and poor fuel efficiency match what others experienced with failing sensors. Even if the wiring check shows no issues, replacing the sensor makes sense given its age and impact on the air-fuel ratio. At around 280 Euro for parts and labor, this seems like a reasonable investment to restore proper engine function. I will update once the repair is complete. Thanks for sharing your experience, it helped confirm my suspicions about the sensor being the root cause rather than just connection issues.

Based on the helpful information and confirmation about exhaust sensor issues, I decided to book an appointment at a repair shop for next week. The steady check engine light and P0172 code, combined with my car never having the O2 sensor replaced in 84277km, make sensor replacement seem like the logical fix. The stronger fuel smell and poor fuel efficiency match what others experienced with failing sensors. Even if the wiring check shows no issues, replacing the sensor makes sense given its age and impact on the air-fuel ratio. At around 280 Euro for parts and labor, this seems like a reasonable investment to restore proper engine function. I will update once the repair is complete. Thanks for sharing your experience, it helped confirm my suspicions about the sensor being the root cause rather than just connection issues.