DTC P0420: Catalyst System Efficiency Below Threshold: Notes
WARNING: This page is about a different car, the 2003 Toyota MR2. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
Heated oxygen sensor for cylinders No. 1 and 4 is referred to as bank 1 sensor 1 and is located at timing chain end of exhaust manifold above catalytic converter. Heated oxygen sensor for cylinders No. 2 and 3 is referred to as bank 2 sensor 1 and is located at flywheel end of exhaust manifold, above catalytic converter.