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:

• IAT greater than 32°F (0°C).
• ECT greater than 167°F (75°C).
• MAF 15-32 gm/s.
• Engine load less than 63 percent and steady.
• Engine speed less than 4000 RPM.
• Conditions present for up to 4 minutes.