Circuit Description

Three-Way Catalyst (TWC) system is used to control emissions. PCM uses signal from Heated Oxygen Sensors (HO2S) to read efficiency of TWC. PCM will set DTC P0420 if TWC oxygen storage capacity is less than a predetermined threshold.

Conditions required to set DTC are: no misfire, fuel trim, injector or ignition control circuit, EVAP, HO2S, VSS IAC, EGR, TP, IAT, MAP, ECT, MAF or CKT DTCs set, engine running longer about 9 minutes, IAT 0-176°F (-18 to 80°C), ECT at 167-248°F (75-120°C), BARO greater than 75 kPa, and system is in closed-loop.