VW Jetta TDI NOx Sensor Troubles & Exhaust Leaks Fix

Had the same problem on a 2006 VW Passat TDI last winter. As someone who regularly does basic maintenance but leaves complex issues to professionals, this one had me worried too. The check engine light kept coming on, and the emission sensor readings were all over the place. Initially thought it was just the sensor, but the workshop found it was actually a damaged wire connection to the NOx sensor near the catalytic converter. The repair was straightforward, they replaced the wiring harness and checked the sensor connections. Total cost was 95€ and took about 2 hours. The air-fuel ratio returned to normal after the fix, and the check engine light stayed off. However, your description of exhaust leakage sounds more extensive than what I dealt with. Could you share: Any specific error codes from the check engine reading? Does the engine performance change when the light comes on? Any unusual exhaust sounds or smells? Have you noticed changes in fuel consumption? This info would help determine if your issue is similar to what I experienced or if you might be dealing with multiple problems in the exhaust system.

Just had my 45000km service last month, and it turned out my issue was more complex. The workshop found that besides the faulty NOx sensor, there was significant corrosion around the exhaust manifold. The air-fuel ratio issues actually stemmed from both the sensor malfunction and the exhaust leak. Total repair ended up at 450€, which included: New NOx sensor, Exhaust manifold gasket replacement, Labor for both repairs The diesel engine runs much smoother now, and the check engine light has stayed off. The repair took a full day, but it was worth fixing both issues at once rather than dealing with them separately. Looking at your exhaust leak symptoms, they sound very similar to what I experienced. Worth checking the entire exhaust system while diagnosing the sensor issue to catch any related problems early.

Thanks for sharing your repair experience. This matches what happened with my Passat too, initially thought it was just a sensor problem but discovered more issues during the repair. After seeing your post, I remember my mechanic mentioning that corrosion near the exhaust manifold is a common issue on these diesel engine models. The air-fuel mixture problems often mask deeper exhaust system damage, which is why emission sensor readings can be misleading. Your repair cost of 450€ actually seems reasonable considering they fixed both the NOx sensor and the manifold issue. My initial 95€ fix for the wiring was just the start, I ended up going back 2 months later for a full exhaust system repair that cost around 400€ when the catalytic converter area started showing similar corrosion symptoms. The pollution control system on these models tends to highlight issues through sensor failure warnings first, even when there are underlying exhaust problems. Fixing everything at once like you did probably saved money in the long run.

Thanks everyone for the detailed feedback. The repair journey was definitely more involved than I initially expected with my Jetta TDI, but I learned a lot about how these systems work together. Quick update: 3 weeks after the repairs, the nitrogen oxide readings are staying consistent and my fuel economy has actually improved. The emission sensor is working perfectly now that both the sensor itself and the exhaust leak are fixed. The workshop explained that the air-fuel ratio problems were causing the engine to run rich, which explains the higher fuel consumption I was seeing before. For anyone facing similar issues, the key takeaway from this thread seems clear, when the check engine light comes on, a failing NOx sensor might just be a symptom of broader exhaust system problems. Getting a complete diagnostic check saved me from having to do multiple repairs. The 450€ spent addressed both the catalytic converter area leak and the sensor failure at once, which turned out to be the right call. Worth mentioning that the engine now runs notably quieter too, something I hadnt expected but definitely appreciate.