VW Transporter NOx Catalyst Issues & Exhaust Leaks Fixed

Had nearly identical issues with my 2003 VW Passat, also with a gas engine. Being someone with some hands-on car repair experience, I initially tried diagnosing the problem myself with a basic OBD scanner. The exhaust leak was quite noticeable, affecting both engine performance and air quality. After the car diagnostics, my trusted workshop confirmed problems with the NOx catalyst and found several connection points in the exhaust system that had corroded. The fix involved: Complete inspection of the exhaust system, Replacement of the catalytic converter, New gaskets and mounting hardware, Post-repair emissions test Total cost came to 265€, which included parts and labor. The repair completely resolved the check engine light and restored proper fuel efficiency. Before suggesting specific solutions for your Transporter, could you share: Current mileage, Whether you hear any specific rattling or hissing sounds, Location of the exhaust leak (front, middle, or rear), Complete error codes from diagnostics, Any recent repairs to the exhaust system This information would help determine if your issue matches what I experienced and whether you might need similar repairs.

My vehicle has 113241km on the odometer. The exhaust leak location seems to be close to the front, producing a clear hissing sound near the engine bay. The nitrogen oxides readings are particularly concerning based on the diagnostics. The error codes specifically point to the NOx catalyst degradation, which matches what you experienced. My last service was just 3 months ago, but no exhaust system work was done then. Before proceeding with a full catalyst replacement, I would like to know if your repair required any additional exhaust system components besides the converter and gaskets? The quoted price seems reasonable if it truly resolves all symptoms.

Thanks for those details, they really help confirm the similarities to what I encountered with my Passat. At similar mileage, my NOx emissions issues were also accompanied by that distinctive hissing from the front section. In my case, the automotive repair did require some additional exhaust system components. While the NOx storage catalyst was the main culprit, we discovered that the exhaust manifold gasket had deteriorated, contributing to the leak. The complete repair included: NOx catalyst replacement, New exhaust manifold gasket, 2 mounting brackets that had corroded, Lambda sensor recalibration The nitrogen oxides readings returned to normal after the fix. No further exhaust leaks or check engine lights occurred in the 2 years since the repair. Car diagnostics now show everything running within spec. Given the matching symptoms and similar vehicle age, I strongly suspect you are dealing with the same core issue. The 265€ I mentioned earlier was just for the catalyst and gaskets. The total with the additional components came to 340€. Just ensure your workshop thoroughly inspects the surrounding exhaust system components while doing the catalyst replacement. This prevents having to go back in for related repairs later.

Thanks for the thorough information. Based on the similar age and symptoms of your Passat, I will move forward with the catalyst replacement and additional exhaust system inspection. Your mention of the manifold gasket issue is particularly helpful since I am hearing that same front-end hissing. I will have my automotive repair shop do a complete assessment of the surrounding components, particularly checking the mounting brackets and sensors. The 340€ total cost seems reasonable for addressing both the nitrogen oxides emissions issues and the exhaust leak problems comprehensively. Will schedule the repair next week and ensure they perform full car diagnostics afterward to verify the fix resolved both the catalyst degradation and air quality concerns. This should hopefully restore proper fuel efficiency and eliminate that check engine light, just as it did in your case. Appreciate you sharing your repair experience, definitely helped confirm this is the right approach rather than continuing to chase individual symptoms.