Audi RS3 Exhaust Leak Linked to NOx Catalyst Issues

I had a similar issue with my 2015 Audi S3, also with a gasoline engine. Having some experience with automotive repair, I can tell you exhaust system problems need proper attention. When my check engine light came on, I noticed a distinct exhaust noise and similar error codes. After inspection, the workshop found a leak where the catalytic converter connects to the exhaust manifold. The nitrogen oxides readings were also off, indicating the emissions system wasnt functioning properly. The repair involved replacing damaged gaskets and tightening all connections in the exhaust system. Total cost was 265 Euro, which included diagnostic work and labor. The catalytic converter itself was actually fine, it was just the connection points causing issues. Before suggesting specific solutions, could you share: Current mileage on your RS3, Exact error codes showing up, Any unusual sounds or smells, Whether performance has been affected, If the exhaust leak sound changes with engine load This information would help determine if your issue matches what I experienced or if you might be dealing with something different in your emissions system.

Thanks for sharing your experience. My RS3 has 34386 KM on the odometer since my last service 3 months ago. The exhaust noise definitely gets louder under load, and I have noticed a slight drop in fuel efficiency lately. The error codes are P0420 and P0421, suggesting catalyst system efficiency below threshold. The symptoms match what you described, especially the distinct exhaust sound from the rear. I am going to get it checked out soon, as NOx emissions issues can worsen air quality and lead to bigger problems if left unchecked. Good to hear your repair was relatively straightforward and didnt require a full catalyst replacement.

Based on those error codes and symptoms, this definitely matches my experience with my S3. The combination of P0420 and P0421 along with decreased fuel efficiency strongly suggests exhaust system leakage at connection points rather than complete NOx storage catalyst failure. Car diagnostics on my S3 showed similar patterns when the leak developed. Given your RS3 has relatively low mileage, a failed catalyst would be unusual. The increased noise under load is a classic sign of an exhaust leak at joining points, identical to what I experienced. The quick drop in fuel efficiency matches my case too, my consumption increased by about 15% before the repair. The workshop found the leak was allowing unmetered air into the exhaust stream, throwing off the sensors and causing those catalyst efficiency codes. Since your symptoms are nearly identical, I would expect a similar repair approach involving gasket replacement and connection tightening should resolve the issue. This is much more cost-effective than replacing the entire catalytic converter. My repair fully restored normal operation and the check engine light hasnt returned in over 12000 KM. Would recommend getting it checked soon to prevent any potential damage to surrounding components in the exhaust system.

Thanks for all the feedback and helpful comparison with your S3 experience. After reading your detailed response, I feel much more confident about the likely cause. The matching symptoms, especially the correlation between engine load and exhaust noise, really help confirm my suspicions. Just scheduled an appointment for next week. I will have them focus on checking the connection points and gaskets first, rather than assuming I need a full catalytic converter replacement. The increased fuel consumption matches your experience too, so hopefully fixing any exhaust leaks will improve both the emissions system efficiency and fuel economy. Your repair costs give me a realistic baseline for budgeting. Will definitely emphasize checking the exhaust system joints and connections when discussing the air quality issues with the technician. Seems much more logical to start with the simple fixes before considering major component replacements in the automotive repair process. I appreciate you sharing the long-term results too, good to hear your repair has held up well over time. Will update once I get the diagnostic results and repair completed.