Audi S8 Engine + Heavy Exhaust Smoke Needs Fixing

I dealt with similar symptoms on my 2019 Audi S6 last season. The symptoms matched exactly, check engine light, rough idle, and strong exhaust smell. The diagnostic revealed a failed oxygen sensor, which was causing incorrect fuel mixture readings. The oxygen sensor malfunction made the engine run rich, pushing excess fuel through the catalytic converter. This explained the strong exhaust fumes. Left untreated, this would have eventually damaged the catalytic converter, turning a manageable repair into a major expense. The repair required replacing two faulty oxygen sensors and cleaning the catalytic converter to remove carbon buildup. This resolved both the performance issues and exhaust smell completely. The catalytic converter showed early signs of damage but was still functional. A qualified technician should perform a full diagnostic test. The exhaust pipe and surrounding components need inspection, as oxygen sensor issues often impact the entire exhaust system. If caught early, you might avoid catalytic converter replacement. Key warning signs that matched in both cases: Rough engine performance, Strong exhaust smell, Check engine light, Increased fuel consumption This is a serious issue requiring prompt attention to prevent damage to more expensive components.

Thanks for sharing that experience. Going through something similar with my Audi S8 now. The check engine light triggered exactly as you described, with the same rough idle and exhaust smell issues. My catalytic converter started showing signs of malfunction last week, and the oxygen sensor readings were way off. Currently waiting on parts for repair. Just curious, do you remember the total cost for fixing both oxygen sensors and cleaning the catalytic converter? Also, has everything been running smoothly since the repair, or have you noticed any other exhaust system issues? My mechanic mentioned checking the EGR valve as well since these problems are sometimes connected. Did they suggest that during your repair?

Good news, I can update you on the full repair outcome for my S6. After seeing the mechanic last week, the exhaust treatment malfunction was completely resolved. The final fix involved replacing a defective Lambda sensor, which cost 375 Euro including labor. The engine light cleared immediately after the repair and the rough running is completely gone. No more exhaust smell issues either. Since the repair, the car runs perfectly smooth with no warning lights or exhaust system problems. My mechanic did a thorough inspection of the catalytic converter and particulate filter while doing the work. Both checked out fine, so no additional repairs were needed. They actually didnt mention anything about the EGR valve, since the NOx sensors and other diagnostic readings showed the issue was isolated to the Lambda sensor. If your mechanic is suggesting an EGR check, it might be worth letting them inspect it while they have everything apart. But in my case, the Lambda sensor replacement alone solved all the symptoms you described.

Thanks for the input. Just wanted to update on how my S8 repair went. Took it to a certified shop last week and the diagnostic confirmed what many here suggested, bad oxygen sensors causing the issues. The mechanic found two failed oxygen sensors and discovered a small exhaust leak near the manifold. They replaced both sensors, sealed the exhaust leak, and performed a complete system diagnostic. The check engine light cleared right after the repair. Total cost came to 850 Euro including parts and labor. While higher than expected, it was worth fixing before it caused catalytic converter damage. The car now runs perfectly, no more rough idle or exhaust fumes. Fuel economy has improved noticeably too. For anyone facing similar issues, getting it checked early definitely saved me from more expensive repairs down the line. The exhaust pipe and all other components checked out fine since we caught it in time.