VW Fox Exhaust Fix: NOx Sensor Troubleshooting Guide

Having dealt with a similar issue on my 2004 VW Polo diesel, I can share some relevant experience regarding sensor failure in the pollution control system. The symptoms you describe sound familiar. My check engine light came on, and the engine was running rough due to an incorrect air-fuel ratio. After scanning, it turned out the wiring harness connecting to the emission sensor was damaged, causing intermittent connection issues. The repair involved: Full diagnostic scan, Testing the sensor connections, Replacing damaged wiring and connectors, Clearing fault codes Total cost was 95€ for parts and labor. The workshop completed the work in about 2 hours. Since the repair, the engine performance returned to normal and the exhaust emissions have been clean. To provide more specific guidance, could you share: The exact error codes from your diagnostic scan, Whether the exhaust leak is visible or just noticeable by smell, If any performance issues occurred before the check engine light, Whether the catalytic converter has been previously replaced These details would help determine if your issue matches what I experienced or if it might be more extensive.

Thanks for sharing the detailed experience. My latest service was 2 months ago, and the NOx sensor readings were normal then. The check engine light started flashing just after hitting 33826km. Since your case involved wiring issues, I checked the connections and noticed some corrosion around the sensor plug. Getting an advanced diagnostic scan tomorrow to compare error codes. The exhaust leak is actually visible as white smoke, unlike your scenario where it was more of a wiring problem. Did your repair shop mention any typical lifespan for these sensors in the exhaust system? Getting concerned this might be a recurring issue requiring regular sensor replacement rather than just a one-time fix.

Thanks for the additional details about your mileage and recent service history. While my wiring issue was fixed relatively easily, your visible white smoke suggests we might be dealing with different problems in the exhaust system. After my initial NOx sensor repair, I discussed sensor longevity with the workshop. They mentioned these emission sensors typically last 60000-80000km under normal conditions. My repair at 45000km was earlier than expected, but the failure was due to wiring rather than the sensor itself. The white smoke in your case points more toward a potential issue with the pollution control system components rather than just sensor failure. When my sensor wiring was faulty, I had error codes but no visible smoke. Corrosion around sensor connections can definitely trigger false readings, but the smoke suggests checking the entire exhaust system thoroughly. My workshop found that proper diagnosis of NOx sensor issues often requires: Testing sensor operation at different engine temperatures, Checking exhaust pressure readings, Verifying all related sensor signals, Inspecting for exhaust leaks around gaskets and joints The advanced diagnostic scan should help pinpoint whether this is truly a sensor issue or something more complex in the exhaust system. Keep us updated with those scan results.

Thanks for the thorough feedback and maintenance history. The white smoke and error codes combined with the corrosion I found make sense now. Will get the advanced diagnostic results tomorrow and post the exact codes. Based on your experience with the emission sensor lifespan estimates, I should probably budget for eventual replacement even if this turns out to be just a wiring issue. The visible exhaust leak definitely seems more serious than your case though. The shop confirmed they can do the full diagnostic testing you mentioned, checking sensor signals at different temperatures and inspecting the entire exhaust system for leaks. Since the check engine light started after such low mileage, I want them to verify if this could be covered under any remaining warranty on the pollution control components. Will update once I have the complete diagnostic report and repair quote. The nitrogen oxide sensor readings and exhaust pressure tests should reveal whether this needs more than just fixing corroded connections.