DTC P0420: Catalyst System Efficiency Below Threshold: Notes

WARNING: This page is about a different car, the 2000 Toyota Corolla. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Heated oxygen sensor No. 1 refers to oxygen sensor closest to engine block. Heated oxygen sensor No. 2 refers to oxygen sensor farthest from engine block.

NOTE: For component location, see appropriate illustration in THEORY & OPERATION article.