BMW 4 Series Exhaust Nightmare: Strong Smells & CEL Alert

Hey! I can relate to your situation. Had similar issues with my 2011 BMW 3 Series last year. The symptoms you're describing, rough running, exhaust smell, and emissions failure, match exactly what happened with my Lambda sensor going bad. When my car acted up, I initially thought it was something major. The exhaust sensor was throwing P0135 and P0141 codes. Mechanic diagnosed it as a faulty Lambda sensor, and mentioned these typically fail between 100-150k km. Had it replaced and the car's been running smooth since then. Not a complex fix, but definitely needs proper diagnosis and genuine parts. Quick tip: Lambda sensors are critical for proper fuel mixture and emissions, so better get it checked soon. A faulty one can lead to increased fuel consumption and potential catalytic converter damage if left too long.

Thanks for sharing your experience! That's really helpful, and it's good to know I'm not alone with these issues. The Lambda sensor definitely sounds like it could be my problem too, especially since the symptoms match up so well. Mind if I ask how much the repair ended up costing you? Also, curious if you've had any other sensor-related problems since getting it fixed?

Hey again! Happy to share an update, got the Lambda sensor replaced and it solved the Exhaust treatment malfunction completely! The repair cost me 375 € and honestly, it was worth every penny. My BMW's running like a dream now, no more check engine light, rough running, or funky exhaust smells. Since you asked, I haven't had any other sensor issues pop up since getting it fixed last year. The car's performance is back to normal, and fuel consumption has actually improved a bit too. Just make sure you get genuine parts, that's super important with these BMWs. If your symptoms are matching what I had, I'd say you're probably looking at the same issue. It's not a complex fix, but you'll want someone who knows what they're doing with BMW electronics. The peace of mind after getting it sorted is totally worth it! Let me know if you need any other info, always happy to help a fellow BMW owner!

Thanks everyone for the advice! Just wanted to update you on what happened. I took my BMW to a different mechanic who specializes in European cars, and guess what? It was indeed the Lambda sensor! The repair was a bit pricey at 425 €, but the difference in how my car runs now is like night and day. The mechanic was super professional and showed me the old sensor, it was completely shot. They explained everything clearly and even showed me what to watch out for in the future. The whole process took about three hours, including diagnostic time. Best part? No more check engine light, the rough running is gone, and that nasty exhaust smell has disappeared. My car passed emissions with flying colors too. Fuel economy has definitely improved, I'm getting about 15% better mileage now. Really glad I asked for advice here instead of going back to my old mechanic. Sometimes paying a bit more for someone who knows what they're doing is totally worth it!