Audi A2 NOx Sensor Failure Causing Exhaust Leaks

Having some experience with similar issues, I faced this exact problem with my 2003 Audi A3 gasoline model. The check engine light came on, and there were noticeable exhaust issues too. The problem turned out to be a faulty connection to the NOx sensor. The workshop found that the wiring harness connecting to the emission sensor had deteriorated, causing intermittent signals. This affected the whole pollution control system, triggering the warning light. The fix was relatively straightforward, they replaced the damaged wiring and connectors to the NOx sensor. The total cost was 95 Euro, which covered both diagnosis and repair. The whole job took about an hour. Before suggesting specific solutions for your case, could you share: Current mileage on your A2, Any other warning lights showing, Whether you notice any performance issues, The exact fault code from the error memory This information would help pinpoint whether your issue matches what I experienced with my catalytic converter monitoring system or if its something else entirely. Make sure your mechanic thoroughly checks all sensor connections in the emission system, not just the obvious components. Sometimes these issues can be interconnected.

Thanks for everyones quick responses. The last service was done at 117977 KM so these issues started shortly after. After thorough checks, the workshop found that the exhaust system needed attention beyond just the emission sensor. The catalytic converter had internal damage, which explained the fault codes and exhaust gas leaks. The nitrogen oxide readings were off because of this damage. The repair cost came to 850 Euro including parts and labor. While expensive, its actually better than initially feared when the check engine light first appeared.

Thanks for the update on your A2. This actually mirrors what happened with my A3 after the initial wiring fix I mentioned. While the sensor connection repair temporarily resolved the check engine warning, I eventually faced a similar catalytic converter failure. The nitrogen oxide readings in my case were also affected by the deteriorating catalytic converter, which threw off the entire air-fuel ratio monitoring system. The repair cost on my vehicle was comparable, around 875 Euro for the complete job. Just to confirm, did they inspect the oxygen sensors while replacing your catalytic converter? In my case, the workshop recommended replacing these simultaneously since they were showing signs of wear and could affect the new catalytic converter's performance. Since both our cars are from the same era, its worth monitoring the exhaust system more frequently now. These components tend to show age-related issues around this mileage point. Regular checks of the emission values can help catch potential problems before they trigger another check engine light.

Thanks everyone for the helpful responses. Want to give you an update on my A2 situation since many asked for details. The final diagnosis confirmed multiple issues affecting the pollution control system. The check engine light was triggered by deteriorating catalytic converter performance, which also caused those exhaust leaks I mentioned. The NOx sensor readings were irregular because of the damaged catalytic converter rather than a sensor problem. The total repair bill was 850 Euro, covering the new catalytic converter, installation, and a thorough check of the air-fuel ratio system. The workshop also inspected all related sensors while doing the work. The repair took longer than expected but they did a complete job. The car now runs much better with no exhaust leaks or warning lights. The emission values are back to normal. While the cost was significant, having a properly functioning catalytic converter and emission system is worth it. Will definitely keep a closer eye on the exhaust system maintenance going forward since these issues seem common in older models.