VW Caddy Exhaust Leak Points to NOx Sensor Issues

Had a similar issue with my 1998 VW Golf, also with a gasoline engine. The symptoms match what I experienced, particularly the check engine light and those exhaust sounds. After some basic troubleshooting, I discovered it was indeed related to the exhaust system, but not exactly what I first suspected. The workshop found a faulty cable connection to one of the sensors, which was causing incorrect readings in the catalytic converter monitoring system. The total repair came to 95€, which included diagnostic testing and fixing the cable connection. This was significantly cheaper than replacing the entire sensor or catalytic converter, which I initially feared might be necessary. Before giving more specific advice, could you share: Is this a gasoline or diesel engine? What specific error codes are you getting? Does the exhaust noise change with engine speed? Have you noticed any changes in fuel consumption? These details would help determine if your issue matches what I encountered. When sensor failure occurs, its often worth checking the simpler possibilities like cable connections before replacing more expensive components in the exhaust system.

Thanks for checking my post. Just wanted to clarify: its a gasoline engine with 138390km on the odometer. The check engine light persists with multiple error codes, including P0420 and P0130. The exhaust noise definitely gets louder when accelerating, and yes, fuel consumption has increased by about 15% over the last month. The NOx sensor seems to be a common failure point according to my research, but the emission sensor readings are all over the place. The pollution control system might need a complete diagnostic. Before taking it to a workshop, Im wondering if cleaning the sensors might help, as suggested in some forum posts. Would that be worth trying first?

Thanks for providing those details. Based on those error codes, your situation is even more similar to what I experienced with my Golf than I initially thought. The P0420 code on my car also indicated catalytic converter efficiency issues, while P0130 pointed to the air-fuel ratio sensor circuit. When I had these exact codes, cleaning the sensors provided only temporary relief. In my case, it turned out the increased fuel consumption and erratic emission sensor readings were caused by a combination of a degraded catalytic converter and a failing oxygen sensor. The complete fix required: 1. Replacing the main oxygen sensor (340€) 2. Installing a new catalytic converter (580€) 3. Full system diagnostic and reset (120€) While cleaning might help temporarily, based on my experience with these specific symptoms and error codes, youre likely facing component failure rather than just dirty sensors. The pollution control system relies heavily on accurate readings, and when the emission sensor starts giving inconsistent data, its usually a sign of sensor degradation. The repair wasnt cheap, but the fuel savings and restored engine performance made it worthwhile. The check engine light hasnt returned since the repair, which was about 8 months ago.

Thanks for the detailed response. This matches up perfectly with what Im seeing with my Caddy. Based on everyones input, it looks like Im dealing with a more serious issue than just dirty sensors. The combination of increased fuel consumption, those specific error codes, and the erratic emission sensor readings point to actual component failure rather than just maintenance needs. Ill skip the sensor cleaning attempt and take it straight to a workshop for proper diagnosis. The potential repair costs you mentioned (around 1040€ total) give me a good baseline for what to expect. Better to address the catalytic converter and air-fuel ratio sensor issues properly than waste time with temporary fixes. Really appreciate the help sorting this out. Its reassuring to know others have successfully resolved similar exhaust system problems. Will update once I get it fixed.