Circuit Description

Three-Way Catalyst (TWC) system is used to control emission. 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 CKP, ECT, HO2S, IAT, MAF, MAP, or TP sensor DTCs set.
• No EGR pintle position, EVAP purge, fuel trim, injector circuit, misfire or VSS DTCs set.
• Converter warm-up test passed.
• Engine speed 1000-3000 RPM.
• Vehicle speed 30-75 MPH.
• PCM determines TWC oxygen storage capacity less than predetermined threshold.