July 1: So it begins. Don't worry, this is not in the correct legal jurisdiction!

DTC P0420: Catalyst System Efficiency Below Threshold: Notes

WARNING: This page is about a different car, the 2004 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: DTC P0420 - Detection Conditions & Possible Causes

Courtesy of MAZDA MOTORS CORP.