Audi Q3 NOx Catalyst Issues and Repair Solutions

Having experienced similar issues with my Audi Q5 2018, I can share some insights from my automotive repair journey. The symptoms you describe match what I encountered, illuminated check engine light and increased NOx emissions due to exhaust system problems. My workshop performed a comprehensive diagnostic test that confirmed the NOx catalyst had deteriorated. The catalytic converter was indeed the culprit, causing both the error codes and the exhaust leaks. The repair involved replacing the complete catalytic converter assembly, which resolved all issues. Total cost was 265 Euro including parts and labor. Before proceeding with repairs, the workshop should: 1. Perform detailed emissions testing 2. Check for exhaust leaks around the catalyst 3. Verify error codes specific to NOx emissions 4. Test the oxygen sensors To provide more specific guidance, could you share: Current mileage on your Q3, Full error codes from diagnostics, Whether you notice any performance issues, If there are any unusual sounds from the exhaust system This information would help determine if your situation matches my experience and whether similar repairs would be appropriate.

Thanks for sharing your repair experience. My Q3 was last serviced at 105000 KM during the scheduled maintenance. For my specific issue, fuel efficiency has noticeably dropped over the past month, accompanied by a slightly rougher idle. The exhaust system also makes a subtle rattling noise when cold. The diagnostics showed error codes P0420 and P0401, pointing to the NOx catalyst efficiency below threshold. I have not experienced any significant power loss, but there is a slight hesitation during acceleration. My dealership quoted 850 Euro for a complete NOx catalyst replacement, which seems quite steep compared to your repair costs. Would you recommend getting a second opinion from an independent workshop specializing in emissions systems before proceeding with the replacement?

Thanks for those additional details about your Q3. The symptoms you describe align closely with what I experienced, though your mileage is a bit higher than when my issues started. The error codes you mentioned are exactly what my diagnostic readout showed too. The price difference is concerning, my 265 Euro repair was at an independent emissions specialist who sources quality aftermarket catalytic converters. Dealership prices for NOx catalyst replacements often run 2-3 times higher due to using only OEM parts. Getting a second opinion is definitely worthwhile. When I faced this decision, I visited a workshop specializing in automotive repair and emissions systems. They performed additional testing that confirmed the nitrogen oxides readings were consistently high and the catalyst was the source. Their diagnostic approach helped rule out related issues like oxygen sensor failures that can mimic catalyst problems. The fuel efficiency drop you mentioned matches my experience too. After the repair, my consumption improved noticeably and the rough idle completely disappeared. The rattling noise is also a typical sign of internal catalyst damage, I had the same sound before replacement. Based on these matching symptoms and my successful repair outcome, I would strongly suggest getting that second opinion from a specialist. They can verify if a full replacement is truly needed and likely offer significant cost savings while maintaining repair quality.

I appreciate the detailed feedback about your repair experience. After hearing about your successful resolution with an independent specialist, I will definitely seek a second opinion. The significant price difference between your repair and my dealership quote of 850 Euro is eye-opening. The matching symptoms, especially the error codes, fuel efficiency drop, and cold start rattling, give me confidence that my NOx catalyst is indeed the root cause. Your confirmation about improved performance post-repair is particularly reassuring. I have already contacted two local shops that specialize in emissions systems and air quality testing. Both can perform comprehensive car diagnostics to verify the nitrogen oxides readings and catalytic converter efficiency before proceeding with any repairs. Based on your experience, I will look for a shop that: Uses quality aftermarket catalytic converters, Performs thorough pre-repair testing, Has specific experience with NOx emissions systems, Offers competitive pricing compared to dealership rates Once I get these additional assessments, I will proceed with the repair at whichever specialist offers the best combination of expertise and value. Thanks again for sharing your repair journey, it has helped guide my decision-making process.