DTC P0420: Catalyst System Efficiency Below Threshold: Notes
WARNING: This page is about a different car, the 2000 Lexus ES 300. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
Bank 1 is also known as right bank (RH). Air/Fuel (A/F) sensor refers to sensor closest to engine block. Heated oxygen sensor No. 2 refers to sensor furthest away from engine block.