Circuit Description

When the rear Heated Oxygen Sensor (HO2S) temperature reaches about 600°F (318°C), it becomes an electrical source that responds to the oxygen content in the exhaust. PCM produces a bias voltage of about 450 mV on the oxygen sensor circuit. When sensor is cold, its internal resistance is extremely high; therefore, the PCM recognizes the bias as an open circuit. As the sensor warms up, the internal resistance decreases. When sensor reaches about 600°F (316°C), it starts producing a voltage based on the oxygen content in the exhaust stream.

DTC will set if HO2S No. 2 voltage is between 391-491 mV for 90 seconds when engine is at normal operating temperature, engine running for over one minute, no other engine sensor or misfire DTC(s) have been set or commanded air/fuel ratio is about 14.7:1. HO2S signal is continuously monitored once these conditions are met.