Circuit Description

WARNING: This page is about a different car, the 2000 Isuzu Hombre. However, it is still accessible from the selected car via links, so may be relevant.

Three-Way Catalyst (TWC) system is used to control emission. Vehicle Control Module (VCM) uses signal from Heated Oxygen Sensor (HO2S) behind TWC to read efficiency of TWC. VCM will set DTC P0420 if TWC oxygen storage capacity is less than a predetermined threshold.

Conditions required to set DTC are:

System in "closed-loop".
Commanded air/fuel ratio is 14.7:1.
Engine run time is 346 seconds.
No CMP, ECT, EGR, EVAP, HO2S, IC or IAC DTCs set.
No IAT, MAF, MAP, TP or VSS sensor DTCs set.
No fuel trim or misfire DTCs set.
ECT is 167-243°F (75-117°C).
BARO is 73 kPa.
Vehicle speed no greater than one MPH.
IAT is 20-167°F (-6.75-75°C).
TP sensor is 1.7 percent or less.
Engine idling at or near specification.
Predicted catalyst temperature is 809°F (475°C) or greater.