Circuit Description

WARNING: This page is about a different variant/trim than selected.

Three-Way Catalytic Converter (TWC) controls emissions of hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx). Catalyst within converter promotes a chemical reaction which oxidizes HC and CO present in exhaust gas, converting them into water vapor and carbon dioxide. Catalyst reduces NOx, converting it to nitrogen. VCM monitors this process using HO2S located in exhaust stream after catalyst.

HO2S produces a signal indicating oxygen storage capacity of catalyst and indicates catalyst's ability to convert exhaust emissions effectively. If catalyst is properly functioning, HO2S signal will be less active than other HO2S located further upstream from catalyst. DTC P0420 will set is HO2S signal is outside of acceptable range for an extended period of time, indicating 3-way catalytic converter oxygen storage capacity is below acceptable threshold.

Conditions for setting DTC:

Engine in "closed loop" fuel control.
Commanded air/fuel ratio equals 14.7:1.
Engine run time equals 346 seconds.
IAT 20-167°F (-6.8 to 75°C).
ECT 167-243°F (75-117°C).
BARO equal 73 kPa.
Predicted catalyst temperature is greater than or equal to 809°F (475°C).
TP sensor not greater than 1.7 percent.
Idle at recommended RPM.
VSS not greater than one MPH.
No transmission related DTCs.
No ECT, HO2S, IAT, MAF, MAP, TP, VSS DTCs are set.
Engine run time greater than 6 minutes.