Audi Q3 Rich Running Issues Solved: O2 Sensor Fix

Had a similar issue with my Audi Q5 2.0 TFSI from 2017. As someone with some experience working on cars, I initially thought it might be related to the oxygen sensor or air filter, but it turned out to be a faulty fuel injector. The symptoms matched exactly, check engine light, poor fuel economy, and inconsistent power delivery. After scanning with an OBD reader, I got multiple codes pointing toward fuel mixture problems. The workshop diagnosed a defective injection valve that was causing too much fuel to enter the combustion chamber. The repair cost me 515 Euro, which included parts and labor. The whole process took about 4 hours at the workshop. Since the fix, fuel economy has returned to normal and the engine runs smoothly again. What diagnostic codes is your OBD reader showing? This would help narrow down whether your Q3 is experiencing the same injector issue. Also, when was the last time you had a full fuel system cleaning service? These cars can be sensitive to carbon buildup, which sometimes masks other problems. To help diagnose this further, could you share: Current mileage, Recent maintenance history, Specific OBD codes, Whether the issues occur more during cold starts or when the engine is warm

I already followed up with a scan and got P0171 and P0507 codes. Latest service was at 101875 KM, where they replaced the air filter and did an oil change. The intake manifold was clean during inspection. After the initial service, I also had the fuel injectors cleaned professionally, but the rich running condition persists. The check engine light stays on constantly now, not just during acceleration. Fuel economy has dropped by about 25% compared to normal. The workshop quoted 800 Euro for diagnostics and potential oxygen sensor replacement. Does this sound reasonable based on the symptoms and codes?

Thanks for the update and OBD codes. On my Q5, I initially got similar codes before discovering the faulty injector. P0171 typically indicates a lean condition, which seems contradictory to rich running symptoms, but this can happen when the oxygen sensor is trying to compensate for other issues. 800 Euro seems high for diagnostics and sensor replacement. For comparison, my complete injector repair including diagnostics was 515 Euro. A single oxygen sensor replacement should cost significantly less. The air-fuel ratio might be off due to a failing oxygen sensor, but with those specific codes, I would suggest having them check: 1. Mass airflow sensor 2. Vacuum leaks 3. Fuel pressure regulator The check engine light staying constantly on and the 25% drop in fuel economy matches what I experienced. However, in your case, since you have already had the injectors cleaned and the intake checked, the oxygen sensor is a more likely culprit. Before agreeing to the 800 Euro repair, consider getting a second opinion focusing specifically on the oxygen sensor circuit. My mechanic initially tested the sensor response before replacement to confirm it was actually faulty. Since the fuel injectors are already clean, addressing the oxygen sensor could resolve your rich mixture issue and restore proper fuel economy.

Thanks for sharing the details of your scan and maintenance history. I ran another diagnostic this morning and still have the P0171 and P0507 codes. Something interesting though, the engine seems to run worse after warming up, which I forgot to mention earlier. Based on your experience with the similar issue and repair costs, I think I will get a second opinion on that 800 Euro quote. A local independent shop specializing in VW/Audi just quoted me 450 Euro for full diagnostics and oxygen sensor replacement if needed. They also mentioned they would check the fuel pressure regulator and vacuum system as part of their standard diagnostic process. The 25% increase in fuel consumption is really hurting my wallet, so I scheduled an appointment for next week. Really hoping it turns out to be just the oxygen sensor affecting the air-fuel ratio. Will update once I know more about what they find. Thanks for sharing the details about your repair, it helped me better understand what to expect and gave me confidence to question that high initial quote.