Exhaust Leak Points to Failing Catalytic Converter

I had a very similar issue on my 2005 Audi A3 1.6L gasoline engine last winter. Having some experience with basic automotive repair, I first tried to locate the leak myself using a smoke test, but quickly realized this needed professional attention. The symptoms matched yours exactly, check engine light and a distinctive exhaust noise during acceleration. Car diagnostics revealed the leak was affecting the NOx catalyst performance. My trusted workshop found the leak was actually at the gasket between the exhaust manifold and the catalytic converter, not the converter itself. The repair involved replacing the gasket and tightening all connections, costing 265 Euro including labor. After the fix, both the noise and check engine light disappeared, and fuel efficiency improved noticeably. To better assist with your case, could you share: Are there any other unusual sounds or performance issues? Have you noticed increased fuel consumption? Did the issue start suddenly or develop gradually? Can you specify which error codes the diagnostic scan showed? This information would help determine if your issue is identical to what I experienced or if it might be something else in the exhaust system.

Thanks for sharing your experience. My last service was at 61000 KM, just 2 weeks ago. The problem started gradually over the past month, and yes, I notice higher fuel consumption recently. The error codes point to catalyst system efficiency below threshold. The exhaust leak definitely impacts air quality when idling in the garage, theres a strong smell. Looking under the car, I can see dark stains around the connection points of the exhaust system. The engine also feels less responsive, especially during initial acceleration. Would it make sense to have the entire exhaust system inspected, since the nitrogen oxides readings are off? Wondering if replacing just the gasket might be enough or if Im looking at a bigger repair.

Yeah, those symptoms definitely sound familiar. After dealing with my A3s issues, I learned that dark stains around connection points often indicate its more than just a simple gasket problem. The high NOx emissions and reduced engine response you describe match what I experienced before things got worse. When my exhaust issues started affecting engine performance, I initially hoped for a quick gasket fix like mine. However, I ended up needing the catalyst replaced too because the leak had allowed excess moisture to damage the NOx storage catalyst over time. Car diagnostics revealed that while the gasket was the initial problem, the catalyst efficiency had degraded beyond acceptable levels. The complete repair including the new catalyst and gaskets cost around 900 Euro, but it completely resolved both the performance issues and emissions problems. Looking at your description, especially the strong smell and stains, I strongly recommend getting a full exhaust system inspection. The recent service might have missed early warning signs of catalyst aging since these issues can develop quickly. The fuel efficiency drop is particularly telling, its a classic sign of a failing NOx system. A proper inspection will reveal whether you can get away with just replacing gaskets or if youll need more extensive repairs like I did. Better to catch it early before it affects other engine components.

Thanks for sharing your experience and advice. After looking at the symptoms more closely, I think youre right about getting a full inspection. The catalyst system efficiency issues combined with the visible exhaust stains and that strong smell in the garage have me worried its more than just a gasket problem. My fuel consumption has definitely gotten worse, Im using about 15% more fuel than normal. The car diagnostics showing NOx emissions problems and reduced catalyst efficiency really point toward a bigger issue with the catalytic converter system, not just a simple leak. I guess Ill bite the bullet and take it to the workshop for a complete exhaust system check. If its going to cost around 900 Euro like in your case, Id rather fix it properly now than risk more engine damage. The air quality issues alone make it worth addressing quickly, especially since I park in an enclosed garage. Thanks again for helping me understand what Im likely dealing with. At least now I can go to the workshop better informed about the potential scope of repairs needed.