Peugeot 107 NOx Catalyst Aging and Exhaust Leak

Hello, I also own a Peugeot 107 and experienced similar issues. The error codes and light are indeed annoying, and yes, an exhaust leak upstream of the catalyst will definitely throw off your emissions readings. Is the leak loud, or more of a subtle hissing sound? It's important to determine the source of the leak - that could cause the NOx catalyst error by allowing unmetered air into the system.

Thanks for the quick reply! The leak isn't super loud, more like a hissing sound. Where should I be looking for the source of the leak? Any common weak points in the exhaust system of the 107?

That hissing points towards a smaller crack or gasket failure. Common spots on the 107 are the exhaust manifold gasket, the flex pipe (if equipped), and any joints between sections of the exhaust. Given the catalyst error, I would highly recommend taking it to a workshop with emissions diagnostic capabilities. They can perform a smoke test to pinpoint the leak and confirm its impact on the catalyst efficiency. I had a similar issue with the exhaust and O2 sensor, and it eventually cost me 265€ to fix.

Thank you, that's super helpful. I'll take it to a local workshop, and let them run a smoke test on it. I really appreciate the advice, I hope I will fix the car soon!