SQ5 Fuel Consumption Spike Points to O2 Sensor Issue

Last month I faced similar symptoms with my 2011 Audi S4. The check engine light came on accompanied by increased fuel consumption. The diagnostic scan revealed problems with the oxygen sensor wiring harness. The root cause was corroded connections at the O2 sensor plug, which led to incorrect air-fuel mixture readings. This triggered the check engine light and caused the engine management system to run rich as a safety measure. The automotive sensor issue required replacing both the wiring harness and the sensor itself. This was a moderate repair that needed professional attention since accessing the connections near the catalytic converter required lifting the vehicle and working with the exhaust system components. The faulty connection was causing the engine computer to receive incorrect readings, leading to poor performance and higher fuel use. Regular car maintenance could have prevented this, the connections had degraded due to heat cycles and exposure to elements. The repair resolved all symptoms: normalized fuel consumption, cleared the check engine light, and restored proper engine performance. For your SQ5, suggest having a professional verify if the O2 sensor electrical connections are intact before replacing components. Sometimes cleaning and reseating the connections can solve the issue without part replacement.

Thanks for sharing your S4 experience. This sounds exactly like what I am dealing with on my SQ5. My fuel efficiency dropped significantly and I am also getting the check engine light warning. I had read about oxygen sensor issues causing incorrect air-fuel ratio readings, which matches these symptoms. Would you mind sharing what the total repair cost was in your case? Also curious if youve had any recurring issues since getting it fixed? Planning to take mine in next week and want to get an idea of the expected costs.

Got good news to share about my S4 repair. After taking it to the mechanic, they found it was indeed just a faulty connection at the oxygen sensor plug, not the sensor itself. The fix only cost 95 Euro for labor to repair the wiring connection. The car maintenance work completely resolved the issues, no more check engine light and fuel efficiency returned to normal levels. Since fixing the aged oxygen sensor connection six weeks ago, everything has been running perfectly. No recurring problems with the air-fuel ratio or any other engine performance concerns. This was much cheaper than replacing the entire oxygen sensor or catalytic converter assembly. Often these sensor-related problems can be solved by addressing wiring issues rather than complete part replacement. The diagnostic scan helped pinpoint the exact connection problem, saving both time and money. Pro tip: when facing oxygen sensor troubles, always have the wiring and connections checked first before assuming you need new parts. A professional inspection of the electrical connections can identify simple fixes that restore proper engine function.

Thanks everyone for the helpful responses. Just wanted to provide an update after getting my SQ5 checked out. Took it to a new mechanic who specializes in European cars. The diagnostic revealed a damaged wiring harness near the O2 sensor, similar to what others experienced. The constant heat cycles had worn down the protective covering, causing intermittent connection issues. The mechanic cleaned the connections and repaired the wiring for 180 Euro plus installed a heat shield to prevent future damage. After the repair, my fuel efficiency immediately improved and the check engine light cleared. The air-fuel ratio is now properly regulated and the engine runs much smoother. The whole repair process took about 3 hours. This was definitely a more reasonable fix than my previous mechanic who wanted to replace the entire oxygen sensor assembly for over 600 Euro. Really glad I got a second opinion and found this forum. The car maintenance costs ended up being much lower than expected.