VW Lupo Diesel NOx Sensor Fault Causing Check Engine Alert

Just dealt with similar emission sensor issues on my VW Polo TDI 2002. The symptoms match what you describe, check engine light with exhaust leaks suggesting catalytic converter problems. The initial diagnosis missed the root cause. After proper testing, it turned out the air-fuel ratio was off due to a faulty nitrogen oxide sensor harness connection. The exhaust system inspection revealed deteriorated wiring near the sensor mounting point. This is actually a common failure point in these engines, the sensor wiring gets damaged from heat exposure and vibration over time. The repair involved replacing the complete sensor assembly and checking the exhaust system integrity since the faulty readings can mask other issues. Not a quick fix but essential to address, failing emission sensors can lead to increased fuel consumption and potential catalytic converter damage if left unchecked. Had to keep the car at the shop for a full diagnostic cycle to verify all exhaust components were functioning properly after the repair. Based on your description, recommend getting a complete exhaust system analysis focusing on sensor functionality and wiring condition. These symptoms rarely fix themselves and usually indicate deeper issues requiring proper diagnostic equipment.

Thanks for sharing your experience with the Polo. Your case sounds exactly like what I am dealing with on my Lupo, especially the part about the air-fuel ratio being affected. Since getting it fixed, have you noticed any other warning lights or exhaust issues? Also, would you mind sharing what the total repair cost was? I want to get a rough idea before heading to the shop, since these NOx sensor replacements seem to vary quite a bit in price.

Got my Lupo back from the shop last week and wanted to update. The NOx sensor failure was exactly as suspected. The mechanic found a damaged cable connection that was throwing off the air-fuel ratio readings. Total repair was 95€ to fix the faulty plug connection, much cheaper than replacing the entire sensor unit. Since the repair, the check engine light has stayed off and the diesel engine runs noticeably smoother. No more exhaust issues or warning lights. The nitrogen oxide readings are now within normal range, and fuel consumption has actually improved slightly. Make sure your mechanic checks the wiring connections first before jumping straight to a full sensor replacement. Often the issue lies in the harness or connector rather than the sensor itself. A proper diagnosis saved me from an unnecessary complete sensor swap.

Thanks to everyone who gave input. After taking my Lupo to a specialized diesel shop, they confirmed the wiring harness issue mentioned here. The mechanic showed me where the NOx sensor cables had degraded from heat exposure, causing inconsistent emission sensor readings. The repair was straightforward, they replaced the damaged wiring section and cleaned the sensor connections. Final cost came to 220€ including diagnostic time. The catalytic converter and rest of the exhaust system checked out fine. Been driving for a week now, no more check engine light and the engine feels more responsive. The shop also showed me the before/after pollution control readings which confirmed everything is working properly. Worth noting they found some minor exhaust leaks at the gaskets which they fixed while in there. Really glad I got a second opinion instead of rushing into a full sensor replacement. Sometimes the simple fix is the right one. My advice is to find a shop that specializes in diesel pollution control systems and will take the time to properly diagnose before replacing parts.