Circuit Description

Three-Way Catalyst (TWC) system is used to control emissions. PCM uses signal from Heated Oxygen Sensor (HO2S) behind TWC to read efficiency of TWC. PCM will set DTC P0137 if TWC oxygen storage capacity is less than a predetermined threshold.

Conditions required to set DTC are:

• No CKP, ECT, EGR pintle position, IAT, MAF, MAP or TP sensor DTCs set.
• No EVAP system DTC set.
• No fuel injector circuit, fuel trim or misfire DTCs set.
• Engine run time greater than 200 seconds.
• HO2S signal voltage stays 425-475 mV.