Conditions for Running the DTC

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

The engine coolant temperature (ECT) is more than 70°C (158°F).
The engine speed is between 2,500-3,000 RPM for at least 3 minutes while driving at certain vehicle speeds.
The engine is operating in Closed Loop.
DTC P0420 runs once per drive cycle when the above conditions have been met.