HO2 Sensor 2

The heated oxygen sensor 2, mounted behind the pup converter, monitors oxygen content in the exhaust to determine the efficiency of the pup converter. This oxygen sensor is used only for converter efficiency, not for air/fuel ratio control. The sensor acts as an electrochemical cell, or battery to produce a voltage in response to the oxygen content in the exhaust. A bias voltage (from the ECM) is between 350 mV and 550 mV and is what the ECM sees when the sensor is inactive or cold. As the heater and the converter temperature heat the sensor up to around 275°C (527°F) the sensor will produce its own voltage to counteract the bias voltage. Low voltage from the sensor indicates high oxygen content (rich mixture). The wires to the sensor carry reference air which is used to compare difference in oxygen from the atmosphere to the exhaust stream.