VW Caddy Exhaust Leak Causes Engine Performance Issues

I experienced very similar issues with my 2021 VW Passat last winter. As someone with moderate experience working on VWs, those symptoms immediately pointed to potential exhaust system problems. The check engine light and rough idle turned out to be related to a faulty lambda sensor. The exhaust smell was quite concerning, and the diagnostic scan confirmed the sensor was sending incorrect readings to the engine control unit. This was affecting the fuel mixture and overall engine performance. I took it to a specialist workshop where they performed a complete diagnostic check. They found the lambda sensor had failed completely and needed replacement. The total repair cost was 375€, including parts and labor. After replacement, the engine light turned off, the rough idle disappeared, and the exhaust smell was gone. Given your symptoms match so closely, I strongly suspect you might be dealing with the same issue. However, these symptoms could also indicate problems with the catalytic converter or an exhaust leak at the manifold. To provide more specific advice, could you share: The engine size and type, How many kilometers/miles on the odometer, Whether you notice any performance changes, If the check engine light is steady or flashing, Any error codes if youve had them read

Thanks for the detailed response. I have 103937km on the clock, and the check engine light remains steady. After reading diagnostic codes with an OBD scanner, it shows P0135 which points to an oxygen sensor malfunction. The exhaust smell seems strongest near the front of the vehicle, and engine performance definitely drops when accelerating. I checked my service records and the oxygen sensor hasnt been replaced since the car was new. The exhaust pipe also shows some surface rust near the connection points, which might explain the leak. Seems like I might be dealing with both a sensor issue and a potential exhaust leak. Given the similar experience you shared, I think Ill have both the oxygen sensor and exhaust pipe connections checked at the workshop. Better to address both potential issues at once rather than having to go back twice.

Thanks for the update on your VW Caddy situation. The P0135 code on your vehicle matches exactly what I encountered with my Passat, definitely points to the oxygen sensor heating circuit malfunction. The exhaust smell location you mentioned near the front is crucial information. In my case, I initially thought it was just the sensor, but the workshop also discovered a small crack in the exhaust pipe near the manifold connection. The surface rust you described is very similar to what I had. The total repair ended up being more than just the sensor replacement I mentioned earlier. The workshop had to repair the exhaust pipe connection and replace the faulty catalytic converter, which had been damaged due to the incorrect fuel mixture caused by the bad sensor. The complete repair including parts and labor came to 890€, but it solved all issues permanently. Your mileage is quite close to when I experienced these problems (mine was at 98000km), and the degradation pattern sounds identical. When they check your vehicle, make sure they inspect the particulate filter as well, these sensor issues can sometimes affect its performance. Based on the error code and symptoms, having both the sensor and exhaust connections checked is definitely the right approach. Let us know what the workshop finds.

Thank you for sharing those details about your VW Caddy situation. The P0135 code from the OBD scanner really confirms the oxygen sensor malfunction I suspected, and having 103937km on the clock makes sense for this type of issue. I checked my service records and realize the oxygen sensor has never been replaced, which explains a lot. The exhaust smell being strongest near the front of the vehicle, combined with the surface rust I noticed on the exhaust pipe connections, suggests I might be dealing with both problems simultaneously. Looking at the repair estimates you shared for your Passat, I should probably budget around 900€ for the worst-case scenario if they find issues with the catalytic converter as well. Planning to have the workshop do a thorough inspection of both the sensor and exhaust pipe connections, might as well tackle everything at once rather than making multiple trips. Thanks again for sharing your experience. Ill schedule the workshop visit this week and make sure they check the EGR valve and particulate filter while theyre at it, since everything seems connected. Will update once I know more about what they find.