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.
• Battery voltage is above 10 volts.
• O2S heater is functioning properly.
• Engine is in closed loop.
• Engine run time greater than 40 seconds.
• HO2S voltage stays 0.426-0.474 volt for 106 seconds over a 125-second period.