Audi Q8 Exhaust Leak Linked to Failed Treatment System

I dealt with a very similar issue on my 2016 Audi Q7 last year. I have some experience working on cars, mainly doing basic maintenance and troubleshooting common issues. The symptoms you describe match exactly what I experienced, rough running engine, check engine light, and strong exhaust smell. In my case, the issue was traced to a faulty lambda sensor. The malfunction was causing incorrect fuel mixture readings, leading to poor performance and the exhaust issues. The repair cost me 375 Euro at a specialized workshop, including parts and labor. They diagnosed it using their diagnostic tool and replaced the sensor. After the fix, all symptoms disappeared and the engine light went off. Before suggesting specific solutions, could you share: Current mileage on your Q8, Whether you have access to an OBD scanner to check error codes, Any recent maintenance work performed, When did these symptoms first appear, Does the engine light stay solid or does it flash The symptoms could indeed point to either the lambda sensor or catalytic converter, but proper diagnosis is crucial since the exhaust system is complex. With more details about your specific situation, I can provide more targeted advice based on my experience.

Thanks for the input. My Q8 has 12465 KM and was last serviced 2 months ago. After reading your experience, I ran a diagnostic scan which showed error codes related to the oxygen sensor circuit. The exhaust leak symptoms and engine light appeared about a week ago. The light stays solid, not flashing. Given the similar symptoms to your case, I will have the oxygen sensor checked first before investigating other potential issues with the exhaust system or NOx sensors.

Thanks for the additional details. Based on the error codes you mentioned and my experience with the same issue, it does sound like the oxygen sensor is the culprit. The solid check engine light and relatively low mileage also align with what I encountered on my Q7. The oxygen sensor malfunction can definitely cause all the symptoms you described, the rough running, exhaust smell, and engine performance issues. When mine failed, it caused incorrect fuel mixture readings which led to poor combustion and that distinctive exhaust smell. Since your car was recently serviced, it would be worth checking if the issue might be covered under warranty. My repair involved replacing the faulty sensor and cleaning the surrounding exhaust components, as the improper fuel mixture had caused some carbon buildup. One thing to note, if left unaddressed, a faulty oxygen sensor can eventually damage the catalytic converter due to incorrect fuel mixtures. The repair costs would be significantly higher if that happens. In my case, catching it early meant only needing to replace the sensor itself. To verify its definitely the oxygen sensor before any repairs, ask the workshop to check the sensor voltage readings. This helped confirm the diagnosis in my situation and ruled out other potential issues with the exhaust system.

Thanks everyone for the helpful information. Just wanted to update, I took the car to the shop today and they confirmed it was indeed the oxygen sensor causing the malfunction. The diagnostic showed the same error codes I got from my scan. They mentioned there was no damage to the catalytic converter or other parts of the exhaust system since we caught it early. The repair cost was 390 Euro and included cleaning some carbon deposits that had built up. The exhaust leak smell is completely gone now and the engine runs smoothly again. The check engine light turned off right after they replaced the sensor. Good thing I addressed this quickly before it could cause more extensive damage to the exhaust system. For anyone encountering similar symptoms, rough engine, exhaust smell, and solid check engine light, definitely get the oxygen sensor checked first. The repair was straightforward and much cheaper than having to deal with catalytic converter issues later.