Audi S6 Exhaust Leak Causing Engine Performance Issues

Had similar issues with my Audi A6 2.0T FSI (2006). Initially thought it was just an exhaust leak, but diagnostic testing revealed multiple problems in the emissions system. The symptoms matched yours exactly, rough idle, check engine light, and strong exhaust smell. The main culprit was a failed Lambda sensor, but there was also carbon buildup affecting the EGR valve operation. The exhaust leak you noticed could be from a cracked catalytic converter housing, which is common on these engines when the emissions system isnt working properly. The repair required: Replacing Lambda sensor, Cleaning EGR valve, Inspecting catalytic converter for damage, Testing NOx sensors, Full emissions system diagnostic This was a serious repair that needed immediate attention. Continuing to drive with these symptoms risks damaging the catalytic converter and could lead to complete engine failure. Would recommend getting a proper diagnostic scan first. The exhaust leak combined with rough running usually points to multiple connected issues in the emissions system rather than just a single failed part.

Thanks for sharing your experience. Very similar to what happened with my S6 last summer. The catalytic converter was indeed cracked, and we also found a significant exhaust leak near the manifold. The particulate filter was completely clogged too, which explained the rough running. Did the repairs hold up well since then? And could you share what the total cost was? Just wondering if prices have changed much since my repair. Also curious if you had any DEF fluid system malfunctions after fixing the main issues, as this was a problem I encountered a few months later.

After getting the repairs done, the exhaust treatment malfunction warning completely disappeared. The Lambda sensor replacement cost 375 Euro and fixed the issue perfectly. The mechanic did a thorough job checking the entire exhaust system, including the catalytic converter and EGR valve connections. Unlike your experience, I havent had any DEF fluid system problems since the repair. The engine light has stayed off and the exhaust pipe is working as it should, with no more leaks or unusual smells. The rough running completely cleared up after the Lambda sensor replacement. Its been over a year now and the repair has held up great. The diagnostic testing confirmed it was mainly the faulty Lambda sensor causing most symptoms, rather than the more extensive issues you encountered with your catalytic converter and particulate filter. Regular maintenance since then has kept everything running smoothly. Just make sure to address any engine light warnings quickly, as waiting can lead to more expensive repairs down the line when exhaust system components start failing in sequence.

Finally got it sorted out properly. Found a certified mechanic who specializes in VAG cars. Initially went in thinking it was just a simple exhaust leak repair, but diagnostic testing revealed the whole mess with the catalytic converter and manifold issues. Total repair came to 2850 Euro including parts and labor. The catalytic converter alone was 1200 Euro, then the exhaust pipe sections and gaskets added another 600 Euro. Labor took about 8 hours since they had to remove multiple components to access everything properly. The DEF fluid system malfunction showed up about 3 months after the main repair. Turned out to be unrelated, just a faulty sensor that cost another 280 Euro to replace. Since then, no more check engine lights or exhaust problems. Definitely learned my lesson about getting proper diagnostics first instead of assuming its just a simple exhaust leak. The rough running completely cleared up after all repairs were done, and the engine performs like new now. Worth every cent compared to risking further damage by waiting.