VW Polo Diesel: Fix NOx Catalyst Issues & Exhaust Leaks

Had almost the exact same issue with my 1999 VW Golf diesel last year. Being fairly experienced with basic car maintenance, I first noticed the problem during a routine check when I spotted visible exhaust leaks near the catalyst. The check engine light triggered several error codes related to the exhaust system. After inspection, the workshop found that the NOx catalyst had deteriorated, affecting both fuel efficiency and NOx emissions significantly. They discovered multiple connection points in the exhaust system had developed leaks due to corrosion. The complete repair involved replacing the NOx catalyst and securing all loose connections in the exhaust system. Total cost came to 265€, which included parts and labor. Since the repair, fuel efficiency improved noticeably and the exhaust leaks stopped completely. To better assist with your situation, could you share: Current mileage on your Polo, Any unusual sounds from the exhaust area, Whether you notice increased fuel consumption, If there are any performance issues, The specific error codes from your diagnostic This information would help determine if your issue matches what I experienced and whether similar repairs might work for you.

Last service was done 2 months ago and showed no issues. Since then covered about 1500km and my current mileage is 36034km. Will get error codes from car diagnostics tomorrow. Thanks for asking these details. Regarding your other questions, yes, fuel consumption increased by about 15% in the last month. Also noticing a rattling sound from underneath, especially when cold starting. Performance seems slightly reduced, particularly when accelerating. Engine feels less responsive than usual. The catalytic converter area does get unusually hot, which I noticed during a recent inspection. The exhaust fumes also have a stronger smell than normal.

Thanks for providing those details. The symptoms you describe are nearly identical to what I experienced with my Golf, particularly the increased fuel consumption and rattling sound. Your mileage is relatively low, but NOx storage catalysts can degrade based on driving conditions and fuel quality, not just distance. The hot catalytic converter area combined with stronger exhaust smell strongly suggests issues with the exhaust system and likely confirms our initial suspicion about the NOx catalyst. In my case, the rattling turned out to be from loose heat shields around the degraded catalyst. Once you get the error codes from car diagnostics, it would be helpful to compare them with what I had. My codes specifically pointed to: NOx catalyst efficiency below threshold, Exhaust system leakage, Lambda sensor malfunction The complete repair on my Golf included: New NOx storage catalyst, Replacement of corroded exhaust clamps, Reseating of heat shields, Basic emissions test after repair Given the matching symptoms, you might want to consider a similar repair approach. The improvement in performance and fuel economy after the fix made the investment worthwhile in my case.

Thanks for sharing those detailed experiences. Your Golf repair situation sounds very similar to what Im dealing with. The symptoms match almost exactly, especially the rattling during cold starts and increased fuel consumption. This gives me more confidence that the NOx catalyst is indeed the core issue. Will get those diagnostic codes tomorrow and compare them with the ones you mentioned. Really helpful to know that the heat shields were part of the rattling problem too, as I was wondering about that sound. The stronger exhaust smell and hot catalyst area match your experience as well. Based on your repair list, I will ask my workshop to specifically check: NOx catalyst condition, All exhaust system clamps, Heat shield attachments, Lambda sensor function The cost seems reasonable considering the improved performance and fuel economy you got after the repair. Will proceed with booking a repair appointment and make sure they do a complete emissions test afterward to verify everything is working correctly. One last question, how long did the complete repair take in your case? Need to plan accordingly for when I take it to the workshop.