VW Touareg NOx Sensor Failure Causes Exhaust Issues

As someone with some experience working on VWs, I had a similar issue with my 2007 VW Passat. The check engine light came on, and I noticed the same symptoms you describe, exhaust issues and error codes related to sensor failures. After scanning the codes at home, I took it to my regular workshop where they diagnosed a faulty connection between the NOx sensor and its plug. The wiring had degraded over time, causing intermittent sensor readings and triggering the check engine light. The total repair cost was 95€, which covered the diagnostic work and fixing the connection. The interesting part was that the initial symptoms pointed toward a catalytic converter problem, but it turned out to be just a wiring issue affecting the pollution control system readings. Getting it fixed quickly was important since faulty sensor readings can lead to poor engine performance and increased fuel consumption. Before suggesting more specific solutions, could you share: Which engine variant your Touareg has? What specific error codes are showing up? Have you noticed any changes in fuel consumption? Does the exhaust smell different than usual? This information would help determine if your issue matches what I experienced or if it might be something more serious in the exhaust system.

Thanks for sharing your insights. I did a full service just 2000km ago, and nothing unusual was found then. The error codes point to the emission sensor area, but the readings are inconsistent. My mechanic says the nitrogen oxide readings fluctuate wildly. The exhaust smell has definitely changed in the last week, becoming more noticeable especially during cold starts. The catalytic converter was actually replaced under warranty back in 2007, but given the age of the car now, I wonder if its starting to fail again. The check engine light stays on constantly now, unlike the initial intermittent flashing. Fuel consumption has increased about 15% since these issues started. Im hesitant to continue driving it much until I know the root cause.

Thanks for those additional details. The constant check engine light combined with the 15% increase in fuel consumption sounds very familiar to what I experienced, but the symptoms suggest a more serious issue than just the wiring problem I had initially. The fluctuating nitrogen oxide readings and stronger exhaust smell, especially during cold starts, often indicate problems with the air-fuel ratio or catalytic converter degradation. Since your catalytic converter was previously replaced, its worth noting these typically last 10-12 years under normal conditions. In my case, after fixing the initial wiring, the problems returned within a month. The final diagnosis revealed that the pollution control system was struggling because the catalytic converter had partially failed. The inconsistent sensor readings were actually a symptom, not the cause. The complete repair ended up costing 850€, including: New catalytic converter, NOx sensor replacement, System diagnosis, Labor costs If you are experiencing similar symptoms to what I had, I suggest getting the catalytic converter tested before replacing any sensors. The diesel engine might be running rich to compensate for the exhaust system issues, explaining your increased fuel consumption. Would you be able to check if theres any black soot around the exhaust pipe? This was another telltale sign in my case that pointed to catalytic converter issues rather than just sensor failures.

Thanks everyone for the helpful information. After reading about your experiences, I decided to have my Touareg thoroughly checked at the workshop today. The diagnostic test confirmed what many of you suspected. The emission sensor system showed multiple faults, but the main culprit is indeed a failing catalytic converter. The nitrogen oxide readings are way off normal parameters, explaining the erratic check engine light behavior. The mechanic found significant deterioration when they inspected the catalytic converter, with visible damage to the honeycomb structure. They quoted 920€ for a complete fix including: New catalytic converter, Replacement of two pollution control sensors, Complete system reset and testing Going to schedule the repair for next week. The diesel engine is still running, but I will limit driving until then to prevent any additional damage. Really glad I asked here first, saved me from potentially replacing parts that werent the root cause. Would be happy to update once the repair is done to confirm if this resolved all the symptoms, especially the fuel consumption issue and exhaust smell.