Audi Q2 Flashing CEL Points to Major Exhaust Issues

I had a similar issue with my Audi Q3 2018 TSI last year, and having some experience with exhaust system problems, I can share what I learned. The symptoms you describe match exactly what I experienced, rough running, check engine light, and exhaust smell. In my case, the oxygen sensor (lambda sensor) was failing, causing incorrect fuel mixture readings. This led to poor combustion and eventually damaged the connection points of the exhaust pipe. The repair involved: Replacing the faulty oxygen sensor, Patching the exhaust pipe connections, Running a diagnostic check on the catalytic converter Total cost was 375 Euro including parts and labor. The repair solved all symptoms, and the engine ran smoothly afterward. Before jumping to conclusions though, could you share: Any diagnostic codes you might have pulled? Does the rough running happen more at idle or during acceleration? Have you noticed increased fuel consumption? When was your last exhaust system inspection? These details would help determine if your issue is identical to what I experienced. The combination of exhaust smell and engine performance issues often points to sensor problems in the exhaust system, but NOx sensors could also be involved depending on your specific model.

Thanks for the detailed feedback. My latest service was 2 weeks ago at 183564 KM. I ran a diagnostic scan and got P0420 code, which points to the catalytic converter. The rough running is definitely worse during acceleration, and fuel consumption has increased by about 15% in the last month. The exhaust leak seems to be getting worse, with more noticeable fumes especially when the engine is cold. The malfunction indicator is now constantly on rather than just flashing. My mechanic initially thought it might be just the exhaust pipe connections, but the symptoms suggest a more serious issue with the catalytic converter system. Would replacing just the catalytic converter be enough, or should I plan for a complete exhaust system overhaul?

Based on the P0420 code and the worsening symptoms youre describing, this definitely sounds more serious than just the exhaust pipe connections I dealt with last year. Since we have similar models, let me share my follow-up experience. After my initial repair, I actually faced a similar P0420 code about 6 months later. The catalytic converter had degraded significantly, and the exhaust treatment system was struggling to maintain proper emissions control. The NOx sensors were giving erratic readings due to the failing catalytic converter. In my case, replacing just the catalytic converter wasnt enough. The entire system needed attention, including: New catalytic converter, Replacement of worn exhaust pipe sections, EGR valve cleaning, Fresh DEF fluid, New particulate filter Total cost came to around 1200 Euro, but it resolved all issues completely. The fuel consumption returned to normal, and the engine performance improved significantly. Given your mileage and symptoms, I would recommend planning for a more comprehensive repair. Replacing just the catalytic converter might temporarily fix the P0420 code, but the exhaust leaks and related issues will likely persist or worsen. Have you noticed any white or blue smoke from the exhaust? This could help determine if theres any internal engine damage contributing to the catalytic converter failure.

Thanks for this thorough response. Since you mentioned blue smoke, I should note that the exhaust is actually quite clean with no visible smoke. This makes me feel a bit better about the engine condition itself. Your comprehensive repair list is particularly helpful. The P0420 code and failing catalytic converter certainly explain my rough running issues. After hearing about your experience, I agree that a complete system overhaul makes more sense than just replacing individual parts. An exhaust leak combined with a faulty catalytic converter would definitely cause my increased fuel consumption and performance issues. The 1200 Euro cost estimate helps with my planning. My mechanic quoted slightly higher at 1350 Euro for a similar scope of work, including: New catalytic converter, Complete exhaust system check and repairs, EGR valve service, All relevant sensor replacements Going to book it in next week. The engine light and rough running are getting worse, so better to fix everything properly now rather than risk more damage. Really appreciate the insights from your similar experience, it helped confirm my suspicions about the catalytic converter being the root cause.