Looking for advice on my 2016 Audi TT with emissions system troubles. The check engine light recently came on and diagnostic scan shows catalyst issues. The exhaust is leaking and NOx catalyst seems to be deteriorating based on readings. Has anyone dealt with similar catalyst aging problems on their TT? Interested in what repairs were needed and how your workshop handled it. Particularly curious about whether a full catalyst replacement was required or if there were other solutions. The car diagnostics point to the NOx storage system, but want to confirm before proceeding with repairs. What were the costs involved in your case?

Audi TT NOx Catalyst Failure: Repair Options & Costs

I had a very similar issue with my 2014 Audi TTS last year, and as someone with moderate experience working on cars, I can share my repair journey. The leak in the exhaust system was affecting the NOx emissions readings and triggering the check engine light. After getting it diagnosed, the workshop found deterioration around the NOx catalyst housing, causing both a leak and reduced catalyst efficiency. The repair cost me 265 Euro, which covered replacing the gaskets and addressing the exhaust leak. This helped restore proper fuel efficiency and brought the NOx emissions back within normal range. Before suggesting specific fixes, could you provide: Current mileage on your TT, Whether you notice any unusual exhaust sounds, If the fuel consumption has increased lately, The exact error codes from the diagnostic scan This information would help determine if your issue matches what I experienced. Sometimes these catalyst problems can be resolved without full replacement, but it depends on the exact location of the leak and the catalyst condition. The workshop should definitely perform a complete exhaust system pressure test to pinpoint the exact location of the leak before proceeding with repairs.

Last service was done at 82000 KM, currently at 83085 KM. The exhaust makes a slight whistling noise under acceleration, and I notice a reduction in engine performance. The diagnostics show P0420 and P0421 codes. The air quality readings from the sensors are getting worse according to the latest scan. My car diagnostics also indicate increased fuel consumption over the past month, jumping from 7.8L/100km to around 9.2L/100km. The automotive repair shop suggested a full inspection of the emissions system before confirming if catalyst replacement is needed. Will keep tracking the NOx emissions values and document any changes in performance until I can get it properly checked next week.

Based on those error codes and symptoms, this definitely matches what I experienced with my TTS. The whistling noise and performance drop are classic signs of an exhaust system leak affecting the catalytic converter function. In my case, the fuel consumption increase was also similar, jumping from 7.6L to around 9.0L/100km. The P0420/P0421 codes were exactly what triggered my check engine light too. After the initial repair I mentioned, I ended up needing a replacement NOx storage catalyst about 2 months later, as the air quality readings kept deteriorating. The complete catalyst replacement was expensive (1850 Euro) but resolved all issues permanently. The car diagnostics afterward showed normal emissions values and the fuel consumption returned to normal. Looking at your mileage, its very close to when my catalyst failed (around 84000 KM). The whistling noise you describe is concerning, in my experience this indicates the leak has likely progressed beyond just gaskets. Would strongly recommend getting the automotive repair done sooner rather than later. Continued driving with a failing catalyst can lead to additional engine damage and even worse fuel consumption.

Thanks for that detailed response about the catalyst replacement experience. My mileage situation does sound very similar to yours. The symptoms match up too, especially that whistling noise and the fuel consumption increase you mentioned. The automotive repair costs you shared are helpful for budgeting. Since my exhaust system problems and NOx emissions issues seem almost identical to what you dealt with, I should probably prepare for a full catalyst replacement rather than just gasket repairs. The air quality readings keep getting worse, so waiting too long could lead to more expensive problems. Will schedule that full inspection for next week and have them do a complete check of the exhaust system components. Better to address these nitrogen oxides issues now before they cause additional engine damage. Thanks again for sharing your repair experience, really helps confirm what I need to do next.