VW Sharan NOx Cat Failure: Real Repair Experience

I dealt with a very similar issue on my 2004 VW Touran diesel last year. Having some experience with basic auto maintenance, I initially thought it was just a loose connection, but it turned out to be more serious. The symptoms matched yours exactly, check engine light, error codes, and visible exhaust leaks. The workshop diagnosed a crack in the exhaust system near the catalytic converter, which was affecting NOx emissions and overall air quality. The repair involved replacing a section of the exhaust system and installing a new catalytic converter. Total cost was 265€ including parts and labor. Since the fix, fuel efficiency improved noticeably and emissions tests have been perfect. Before offering more specific advice, could you share: Current mileage on your Sharan? Are you noticing any specific smells from the exhaust? Does the engine sound different than usual? Have you had any previous repairs to the exhaust system? This information would help determine if your issue is similar to what I experienced with my Touran. The automotive repair process might vary depending on these factors.

Thanks for sharing your experience with the Touran. My Sharan has 10645km since the last major service. We did notice a distinct sulfur smell lately, and the engine does sound louder than normal, especially during cold starts. The car diagnostics from my regular workshop showed P0420 and P0401 error codes. They suggested a complete emissions system inspection might be needed. I appreciate the cost reference point, 265€ seems reasonable if the repair scope is similar. Checking for exhaust leaks near the NOx catalyst seems like a good starting point based on your experience. Will schedule a thorough inspection of the exhaust system components this week. Did your fuel consumption improve significantly after the repairs? Currently getting much worse efficiency than usual.

Thank you for those additional details about your Sharan. The sulfur smell and increased engine noise definitely mirror what I experienced with my Touran before the repairs. The P0420 code typically indicates catalytic converter efficiency below threshold, which matches my case exactly. The exhaust leak in my Touran was causing the NOx emissions control system to work inefficiently, leading to poor fuel economy. After fixing the cracked exhaust system and replacing the catalytic converter, my fuel consumption improved by roughly 15%. The sulfur smell disappeared completely, and the engine noise returned to normal levels. The car diagnostics showed no more error codes. Based on your symptoms and error codes, it sounds nearly identical to my situation. With 10645km since the last service, deterioration of the emissions system components wouldn't be unusual. A thorough inspection focusing on the catalytic converter and surrounding exhaust system components should reveal the extent of the problem. Make sure they check for any hairline cracks that might be allowing exhaust gases to escape, these can be tricky to spot but significantly impact performance.

Thanks for the detailed follow-up information. Those specific diagnostic codes and symptoms match what my mechanic told me too. The fuel consumption issues are particularly concerning, my workshop mentioned that poor efficiency is often linked to problems with the NOx catalyst and overall emissions system performance. The mileage since my last service is similar to yours, and the same sulfur smell was present in my case. I will definitely proceed with the complete inspection you suggested. The prospect of a 15% improvement in fuel efficiency after repairs makes the investment worthwhile. I have scheduled the inspection for the exhaust system and NOx catalyst components this week. The estimated repair cost from my workshop aligns with your experience at around 265€, which seems fair for the scope of work needed. Will make sure they thoroughly check for those hairline cracks you mentioned in the exhaust system. Getting this fixed properly should help restore proper emissions control and resolve the engine noise issues during cold starts. Looking forward to having this resolved and getting back to normal fuel consumption levels. Thanks again for sharing your repair experience, it has been very helpful in understanding what to expect.