Audi A5 NOx Catalyst Issues Need Urgent Fix

As someone with moderate experience maintaining Audis, I faced a similar issue with my 2019 Audi A4. The symptoms you describe match exactly what I encountered, check engine light and noticeable exhaust fumes. After inspection, my workshop found a leak where the catalytic converter connects to the exhaust manifold. Poor air quality and decreased fuel efficiency were immediate signs something was wrong. The repair involved replacing gaskets and tightening all connections around the catalytic converter area, costing 265 Euro in total. The fix completely resolved the NOx emissions issues and the check engine light hasn't returned in months. The workshop also performed a thorough diagnostic scan to ensure no other components were affected. To better assist, could you share: Current mileage on your A5, When you first noticed the exhaust leak, Any unusual sounds from the exhaust system, Whether fuel consumption has increased, If the car underwent recent maintenance This information would help determine if your issue matches what I experienced or if it might be something different in the exhaust system.

Thanks for the detailed response. My A5 has 48491 KM on the odometer, with the last service completed just two months ago. The exhaust leak and check engine light started about a week after that service. I notice a slight rattling noise from the catalytic converter area during cold starts. Based on your experience, it sounds like I might have a similar connection issue. The car diagnostics also showed slightly elevated NOx emissions readings, which aligns with your description. I will have the workshop check those specific connection points first.

Having gone through this myself with my A4, the timing of your symptoms right after service is noteworthy. The rattling during cold starts particularly stands out, as this was also a telltale sign in my case before the full exhaust leak developed. Your mileage is similar to when my issue occurred at 51000 KM. The elevated NOx emissions combined with the rattling strongly suggest a deteriorating connection between the exhaust manifold and catalytic converter, just as I experienced. Since you mentioned getting slightly elevated readings, I recommend having them specifically check: All mounting brackets around the catalytic converter, The connection points between exhaust components, The condition of the heat shields, The oxygen sensors near the catalyst In my case, fuel efficiency improved noticeably after the repair. Keep monitoring your fuel consumption, if it starts increasing, it further confirms the exhaust system leak diagnosis. The complete resolution of my NOx emissions issues after fixing these connection points suggests you might be looking at a similar straightforward repair rather than full catalytic converter replacement.

Thanks everyone for your advice and knowledge sharing. After tracking my fuel consumption more closely this week, I noticed a 15% increase compared to normal. The symptoms you described match my situation perfectly, especially regarding the connection issues between the exhaust manifold and NOx catalyst. I have scheduled an appointment with my workshop and specifically requested them to inspect the mounting brackets and connection points in the emissions system. They will run a complete car diagnostics check, focusing on the catalyst area and nearby sensors. The service advisor mentioned they frequently see similar nitrogen oxides related issues on these models, often fixable without major component replacement. Will update once they complete the inspection and repairs. Hopefully it will be a straightforward fix like in your case rather than requiring a full catalyst replacement. Really appreciate the detailed technical insights that helped me better understand the likely root cause.