Laguna NOx Catalyst and Exhaust Leak

I had a similar experience with my Laguna – though not the exact same year. A leak upstream of the catalytic converter can definitely mess with the readings and throw off the NOx catalyst efficiency. Think of it like trying to measure ingredients for a cake, but some flour is spilling; you'll never get the right mix. Have you checked for any obvious cracks or holes in the exhaust manifold or piping?

Thanks for the insight. I visually inspected the exhaust manifold and piping but didn't find any obvious cracks or holes. Where else should I look to find this leak?

Sometimes it’s not visible. It could be a small crack or a failing gasket, especially around joints or flanges. Think of it like a slow puncture in a tire; you can't see the hole, but the pressure drops. Given the NOx catalyst issue, it's probably best to get it smoke-tested by a workshop. They can pinpoint the leak accurately.

I appreciate the advice. I took the vehicle to a workshop, and a small leak in the exhaust system was found. The repair, including parts and labor, was 265€. The error code is now gone. Thanks for your help!