Lexus RX NOx Catalyst Error and Exhaust Leak

I had similar symptoms in my RX. An exhaust leak upstream of the catalyst can throw off the readings and cause that NOx code. Do you hear the leak, or did you just find it while poking around?

I hear the leak. Could this exhaust leak really be the main cause of the NOx storage catalyst error, or is the catalyst itself more likely failing because of age and mileage?

In my case, repairing the exhaust leak resolved the NOx code. The leak messes with the oxygen sensors, and the ECU interprets that as a catalyst issue. I'd advise getting the exhaust leak professionally inspected and repaired before assuming the worst about the catalyst. The repair at the workshop was around 265€. It's worth addressing before further diagnostics or catalyst replacement.

I appreciate the detailed explanation and advice. I will schedule an appointment with a qualified mechanic to inspect and repair the exhaust leak promptly. Hopefully, this will rectify the NOx storage catalyst error as well. Many thanks for your help!