Failing NOx Catalyst: GTV Repair Guide & Costs

Having dealt with a similar issue on my 2003 Alfa Romeo 156, I can share my experience with exhaust system problems. With some experience working on Alfa Romeos, these symptoms often point to issues with the catalytic converter and NOx catalyst system. My car showed the same symptoms: check engine light and noticeable exhaust leaks. The workshop performed a comprehensive diagnosis of the emissions system and found deterioration in the NOx catalyst, along with a significant leak where the catalyst connected to the exhaust manifold. The repair involved: Full diagnostic scan, Visual inspection of the exhaust system, Emissions testing, Replacement of worn gaskets, NOx catalyst replacement Total cost came to 265 Euro, which included parts and labor. After the repair, engine performance improved noticeably, and the exhaust noise disappeared completely. To provide more specific advice for your GTV, could you share: Current mileage, Any performance changes you noticed, Exact error codes from the scan, Whether you notice the exhaust noise at specific RPM ranges The nitrogen oxides reduction system can be quite complex, and symptoms can vary between models, so these details would help determine if your issue matches what I experienced.

Following up on the catalyst issue, after my latest service at 129017 KM, the workshop confirmed the NOx catalyst was severely degraded. The new part really made a difference in reducing nitrogen oxides and improving fuel efficiency. The exhaust system runs much quieter now and the check engine light has stayed off. The repair cost was reasonable at 315 Euro plus labor. Just make sure to use an OEM catalyst to maintain proper emissions control.

Thanks for the update on your GTV catalyst replacement. My 156 also showed significant improvements after the NOx catalyst repair, especially in terms of emissions system performance. The workshop confirmed my old catalyst was operating at less than 60% efficiency through their car diagnostics tests. Like your case, I noticed the fuel consumption dropped noticeably after the repair. The catalytic converter and entire exhaust system now work together properly, which has really helped with air quality compliance and overall engine performance. The price difference between our repairs likely comes from the slight variations in parts costs between models, but both seem reasonable for an OEM component. My 156 has now run trouble-free for 45000 KM since the repair, with consistent emissions test results. Have you noticed any other performance improvements since the repair? My throttle response became much smoother, especially during cold starts.

Thank you everyone for the advice. After completing the full repair, I can confirm the NOx catalyst replacement was exactly what my GTV needed. The workshop found the old catalyst was severely deteriorating, affecting both emissions control and engine performance. The new OEM part made an immediate difference, exhaust leaks gone, check engine light cleared, and better fuel economy. Total repair costs came to 315 Euro plus labor, which seems fair given the improved air quality and performance gains. The emissions system now works perfectly and cold start performance is much smoother. After 2000 KM with the new catalyst, fuel consumption has dropped by about 8%. For anyone facing similar NOx emissions issues on older vehicles, I strongly recommend getting a proper diagnosis and using quality parts. The difference in engine response and overall performance makes the investment worthwhile.