Heated Oxygen Sensor

CAUTION: Measure HO2S voltage with a Digital Volt-Ohmmeter (minimum 10-megohm impedance) only. Current drain of a conventional voltmeter could damage sensor.

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started the ECM operates in an open loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The ECM supplies the HO2S with a reference or bias voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in closed loop. High HO2S voltage output indicates a rich fuel mixture; low HO2S voltage output indicates a lean fuel mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. If ECM detects an active HO2S voltage signal below a calibrated minimum amplitude, a DTC will set.

Each HO2S has an HO2S high signal circuit, HO2S low signal circuit, HO2S heater ignition 1 voltage circuit, and HO2S heater low control circuit.