RS3 Exhaust Leak Causes Power Loss and Engine Issues

I had a very similar issue with my 2016 RS4. With some experience working on cars, I can share what happened in my case. The symptoms matched exactly what you describe, rough running, check engine light, power loss and exhaust odor. The issue turned out to be a faulty oxygen sensor, which was interfering with the fuel mixture and causing poor performance. My workshop ran a diagnostic scan that pointed to the lambda sensor readings being out of range. They confirmed this by checking the sensor values at different engine speeds. The repair involved replacing the oxygen sensor and clearing the error codes. Total cost was 375 Euro including parts and labor. These symptoms could also indicate problems with the catalytic converter or EGR valve, which can show similar warning signs. To help diagnose your specific case, could you share: Current mileage, Any recent repairs or maintenance, Whether the check engine light is solid or flashing, If the problem started suddenly or developed gradually Without proper diagnosis, running the engine with these symptoms risks damaging other components in the exhaust system, particularly the catalytic converter which is much more expensive to replace.

Thanks for your detailed reply. My car has 66954 KM and had its last service 3 months ago. The check engine light came on suddenly during highway driving and has remained solid since then. Running a basic OBD scan showed P0420 code, suggesting catalyst system efficiency below threshold. Given the symptoms and the exhaust leak sound, this could point to multiple issues beyond just the oxygen sensor. I will have the exhaust system properly inspected, particularly around the NOx sensors and potential exhaust leaks. The sudden power loss and rough running is concerning, and I want to prevent any additional damage to the catalytic converter or EGR valve.

Thanks for the additional details. That P0420 code alongside the symptoms definitely narrows things down. When my RS4 showed similar issues, I initially thought it was just the oxygen sensor, but it turned out the catalytic converter was also damaged. The sudden onset during highway driving matches my experience, these issues often show up under sustained load. In my case, the exhaust pipe had developed a small crack near the catalytic converter, allowing exhaust gases to escape. This triggered the check engine light and caused the engine to run rough due to incorrect sensor readings. After a proper inspection, I ended up replacing: Both oxygen sensors (pre and post cat), The damaged section of exhaust pipe, The catalytic converter, which had internal damage Total repair cost was around 2200 Euro, but it completely resolved the power loss and rough running. The EGR valve was tested but worked fine. If your DEF fluid level is good and the exhaust leak is caught early, you might avoid the more expensive catalytic converter replacement. Would recommend getting it checked soon, the longer you drive with the exhaust leak, the higher the risk of damaging other components in the system.

Thanks for the comprehensive feedback on your RS4 experience. My case does seem quite similar. Good point about the exhaust pipe potentially being cracked near the catalytic converter, that would explain both the leak sound and the P0420 code. Based on your repair details, I will prioritize getting a full inspection of the exhaust system, focusing on the oxygen sensors, exhaust pipe integrity, and catalytic converter condition. The cost breakdown you provided helps set realistic expectations for potential repairs. Since my issue also started suddenly during highway driving, and given the similar symptoms, I suspect I might be looking at multiple component replacements like in your case. Still hoping its just an exhaust leak and sensor issue rather than a full catalytic converter replacement. Going to schedule an inspection this week before any highway driving. The rough running and power loss make me concerned about causing additional damage, especially to the catalytic converter or EGR valve. Will get both pre and post cat oxygen sensors checked as well since they could be contributing to the efficiency code.