Audi S3 Cat Converter Failing + Exhaust Leak Alert

Had a similar situation with my 2015 Audi S4 last year. The exhaust leak combined with catalyst issues created multiple error codes during car diagnostics. The NOx emissions were far above acceptable levels, indicating the NOx catalyst was severely degraded. The main problem was a cracked flex pipe leading to the catalytic converter, which allowed exhaust gases to escape before proper treatment. This leak also put extra stress on the catalyst system, accelerating its wear. The nitrogen oxides readings were consistently high even after the leak repair, confirming the catalyst needed replacement. This isnt a minor issue, driving with a failing catalytic converter can cause serious engine performance problems and reduced fuel efficiency. The exhaust leak can also allow harmful gases into the cabin. The repair involved: Full inspection of exhaust system, Replacement of damaged flex pipe, Installation of new catalytic converter, Recalibration of engine management system, Post-repair emissions testing The whole job took two days to complete properly. These issues are relatively common in higher mileage Audis from this generation, especially if regular maintenance wasnt followed.

Thanks for that detailed reply. Sounds exactly like what Im experiencing with my S3, down to the flex pipe symptoms. My check engine light has been erratic too, sometimes going off and coming back on during longer drives. Since your repair was recent, do you remember the total cost breakdown? Also curious if youve had any other emissions-related issues pop up since the catalytic converter replacement? The car diagnostics at my local shop showed similar nitrogen oxides problems, but they seemed unsure about the root cause. Your experience gives me a clearer picture of what to expect for the automotive repair process. Really helps to hear from someone whos been through it.

I got the repairs done about 8 months ago and everything has been running perfectly since then. The car diagnostics confirmed that fixing the exhaust system leak and addressing the NOx storage catalyst aging completely resolved the issues. Total cost came to 265 Euro for the exhaust leak repair, which was actually less than expected. The emissions system is now working exactly as it should, no more erratic check engine lights or nitrogen oxides problems. The catalytic converter performance returned to normal once the leak was fixed, so I didnt need a full replacement after all. This saved significant costs since the leak was causing the system to show false readings. Regular monitoring shows all emissions levels are now within proper range. If your symptoms match what I experienced, getting that flex pipe fixed should be your first step before considering a complete catalytic converter replacement. One thing I learned is that proper car diagnostics are crucial, my initial high NOx readings were mostly due to the exhaust leak rather than a failed catalyst. Worth making sure your shop does thorough testing to identify the true root cause.

Thanks everyone for the advice! Just wanted to update on how things turned out. Finally got my S3 fixed last week after finding a reputable automotive repair shop that specializes in emissions systems. The car diagnostics revealed exactly what was discussed, a damaged flex pipe was causing the exhaust leak, throwing off the catalytic converter readings. The mechanic did a thorough inspection of the entire exhaust system before starting any work. Thankfully, my NOx catalyst was still functioning properly once they fixed the leak. The repair took about 6 hours total and cost 310 Euro, which included: Flex pipe replacement, Full emissions system testing, Labor costs, New gaskets and hardware The check engine light is now completely gone and the engine runs much smoother. No more strange noises from the exhaust either. Really glad I got a second opinion instead of rushing into a full catalytic converter replacement at my old shop. Thanks again for helping me understand what to look for. Having this knowledge made me feel much more confident when discussing the repairs with the new mechanic.