Heated Oxygen Sensor

CAUTION: Measure oxygen sensor voltage with a digital volt-ohmmeter (minimum 10-megohm impedance) only. Current drain of a conventional voltmeter could damage sensor.

Heated Oxygen Sensor (HO2S) is used for fuel control and post catalyst monitoring. Each HO2S compares oxygen content of he surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The PCM supplies the HO2S with a reference or bias voltage of about 450 mV. When engine is first started, PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and closed loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates at greater than or less than bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream.