P0420 OBD Trouble Code

Catalyst System Efficiency Below Threshold

Catalyst Efficiency Below Normal Conditions

Engine running in closed loop for 3 minutes, ECT sensor input over 147°F, engine speed from 1200-1700 rpm with throttle open, VSS over 20 mph, MAP sensor at 1.5-2.0v, then the PCM detected that the switch rate of the rear HO2S-12 reached 70% of the front HO2S-11 switch rate.

Catalyst System Efficiency Below Threshold Conditions

Engine running at steady state highway conditions for 5 minutes in closed loop, then the PCM detected that the rear HO2S switch rate was too high

Catalyst System Low Efficiency Conditions

No PCM codes set, ECT input over 167°F, IAT input over O°F, MAF input 12-32 g/sec, engine speed below 4000 rpm, engine load under 63% and steady for 4 minutes, then engine speed at 1000-3000 rpm and VSS at 30-75 mph and the PCM detected that the catalyst O2 storage capacity was below an acceptable level

Catalytic converter - Bank 1 - efficiency below limit

Catalytic converter, wiring, intake/exhaust system, injector, ECM