VW Taos NOx Sensor Issues Trigger Check Engine Light

I had a very similar issue with my 2020 VW Tiguan last winter. Having some experience with emission system repairs, I knew it was important to address this quickly to avoid potential damage to the catalytic converter. The check engine light came on and the diagnostic showed emission-related codes. Initially thought it was the nitrogen oxide sensor failing, but after inspection, the workshop found it was actually just a loose connection in the wiring harness near the air-fuel ratio sensor. The cables had some wear and the connection needed cleaning and proper securing. Total repair cost was 95€ which covered diagnostic and fixing the cable connection. The workshop managed to complete everything in about 2 hours. Since the repair, the emission system has been working perfectly with no check engine lights. To help provide more specific advice for your case, could you share: Have you scanned for specific error codes? Are you noticing any changes in fuel consumption? Does the check engine light stay constant or does it flicker? Are there any unusual sounds from the exhaust area? These details would help determine if your issue matches what I experienced or if it might be something different in the pollution control system.

Thanks for sharing your experience. My car just had its 80000km service last month, and since then the NOx sensor seems to be acting up. The error code reader shows P0420, pointing to the emission sensor circuit. The check engine light stays constant and fuel consumption remains normal. No unusual sounds from the exhaust, but the onboard computer indicates higher emission values than usual. Spoke with another Taos owner who suggested the sensor failure might be causing the pollution control system to malfunction. Before booking a workshop appointment, I wanted to check if cleaning the sensor connections might resolve the issue, similar to your experience with the wiring harness. Would you recommend trying this first, or should I have the entire emission control system checked professionally given the mileage?

Thanks for those additional details. Unlike my Tiguan case where it was just a wiring issue, your P0420 code and the higher emission values suggest this might be more than just a connection problem. In my follow-up experience with the diesel engine system, I learned that attempting to clean sensor connections on modern emission systems can sometimes cause more harm than good. After my initial wire harness fix, I actually encountered a similar P0420 code about 6 months later. The exhaust system inspection revealed that while the NOx sensor was reporting issues, the root cause was actually carbon buildup affecting the pollution control components. The workshops diagnostic showed the sensor was functioning correctly but responding to actual emission issues. The full repair included: Complete emission sensor testing, Exhaust system inspection, Carbon deposit cleaning, Software update for the pollution control module Total cost was 450€, but it resolved the issue completely. Given your cars mileage and the specific error code, I would recommend having it professionally diagnosed rather than attempting sensor cleaning yourself. Modern emission systems are quite complex and interconnected. Do you notice any loss in power during acceleration? This could help confirm if its purely a sensor failure or a broader exhaust system issue.

I really appreciate the detailed comparison with your follow-up repair experience. The fact that your initial wire fix led to a deeper emission system issue later makes me think I should take the professional route rather than attempt any DIY fixes. My Taos does occasionally feel slightly sluggish during hard acceleration, which based on your experience might indicate more than just a sensor failure. The check engine light problem combined with the P0420 code and performance issues suggests the catalytic converter might need inspection too. Given the complexity of modern pollution control systems and the potential for causing more damage, I will schedule a complete diagnostic at the workshop. The 450€ repair cost you mentioned seems reasonable if it includes a thorough system check and necessary cleaning of emission components. Will make an appointment for next week and make sure to request: Full emission sensor diagnostic, Catalytic converter efficiency test, Check for carbon deposits, Emission control system software verification Better to address this properly now than risk more expensive repairs later. The detailed breakdown of your repair experience really helped make this decision clearer.