Failing NOx Catalyst Triggers Audi A1 Exhaust Issues

Having some experience with exhaust system repairs, I faced a similar issue with my 2018 Audi A3. The symptoms you describe match what I encountered, check engine light and NOx catalyst related codes during car diagnostics. My workshop identified a leak in the exhaust system that was affecting the NOx catalyst performance and overall air quality. The repair involved replacing damaged exhaust components and the catalyst itself to restore proper fuel efficiency and emissions control. The total repair cost was 265 Euro, which included parts and labor. After the fix, the nitrogen oxides readings returned to normal and the check engine light has stayed off. The repair has held up well since then. To provide more specific advice for your case, could you share: Current mileage on your A1, Whether you notice any performance issues, If there are any unusual sounds from the exhaust, When the check engine light first appeared, If you smell exhaust fumes inside the cabin These details would help determine if your issue is similar and if the same repair approach might work.

Thanks for the detailed reply. My A1 has 10437 KM and the last service was just 2 months ago. I do notice a slight rattling sound from under the car, especially when cold. The check engine light started flashing last week, and there is a faint exhaust smell when idling. The catalytic converter and NOx catalyst system should still be in good condition given the low mileage, which makes me wonder if there might be physical damage causing these emissions issues rather than normal wear. I have not noticed any significant changes in performance, but I am concerned about the impact on air quality if left unaddressed.

Thanks for those additional details. After fixing my A3's similar issue, I can confirm that physical damage could definitely be the culprit, especially with the rattling sound you mentioned. The low mileage on your A1 supports this theory since NOx storage catalysts typically don't deteriorate this quickly. The exhaust smell during idling combined with the rattling suggests a possible crack or loose connection in the exhaust system near the catalytic converter area. On my A3, the workshop found that road debris had caused minor damage, creating a small leak that affected the NOx emissions readings and triggered the check engine light. From my repair experience, I recommend getting car diagnostics done soon, as these symptoms closely match what I experienced before more serious issues developed. The workshop should perform a thorough inspection of the entire exhaust system, particularly checking for: Loose mounting brackets, Hairline cracks in connections, Impact damage to the catalytic converter housing, Proper sensor function in the NOx catalyst system When my A3 was repaired, catching it early helped avoid more extensive damage to the emissions control systems. The repair cost I mentioned earlier was lower because only localized damage needed fixing rather than full component replacement. If you hear the rattling getting worse or notice stronger exhaust smells, consider getting it checked immediately rather than waiting for your next scheduled service.

Thanks everyone for the helpful replies. Given what you shared about physical damage being a likely cause, I will schedule an appointment with my workshop this week. The rattling sound seems to be getting more noticeable, so I want to have the car diagnostics done before any serious damage occurs to the emissions system. I will ask them to specifically check the catalytic converter and NOx catalyst components for impact damage or loose connections, since this appears to be the most probable cause given my low mileage. The nitrogen oxides readings from my diagnostic tool combined with the exhaust smell definitely suggest a leak that needs addressing. Will update once I know more about the repair costs and what exactly they find. Really hoping it is just a minor fix like a loose bracket or small crack rather than needing full component replacement.