DTC P0420: Catalyst 1/1 Efficiency Failure: Description

Catalytic converter efficiency is monitored after engine warms up to 147°F (64°C), throttle has been open for 180 seconds when vehicle speed is more than 20 MPH, with engine speed at 1200-1700 RPM and MAP vacuum 15-21 in. Hg. DTC will set when PCM senses catalyst efficiency deteriorated to a predetermined value. Possible causes are: defective catalytic converter, exhaust leak, engine mechanical problem or lazy upstream Heated Oxygen Sensor (HO2S).