Monitored & Set Conditions

WARNING: This page is about a different car, the 2003 Dodge Dakota. However, it is still accessible from the selected car via links, so may be relevant.

DTC P0420: CATALYST 1/1 EFFICIENCY - Catalytic converter efficiency is monitored after engine warm up to 158°F (70°C), 180 seconds of open throttle operation, at a speed 18-55 MPH, with the engine at 1200-1700 RPM and MAP vacuum 15.0-21.0 in. Hg. DTC will set when catalyst efficiency deteriorates, when the switch rate of the downstream O2 sensor approaches that of the upstream O2 sensor. If at any point during the test the switch ratio reaches a predetermined value a counter is incremented by one.

DTC P0421: WARM UP CATALYST 1/1 EFFICIENCY BELOW THRESHOLD OR DTC P0432: WARM UP CATALYTIC 2/1 EFFICIENCY BELOW THRESHOLD - Catalytic converter efficiency is monitored with the engine running. DTC will set when the Powertrain Control Module doesn't recognize the catalytic converter warming up efficiently.