Heated Oxygen SEN (HO2S) Bank 1 SEN 2 & HO2S Bank 2 SEN 2

The heated oxygen sensor bank 1 sensor 2 (cylinders 1, 3, 5 which are closest to the front of dash) or heated oxygen sensor bank 2 sensor 2 (cylinders 2, 4, 6 which are closest to the radiator) are both located in each exhaust pipe downstream from each pre-catalytic converter. The functions of the sensor are to monitor the efficiency of each pre-converter and for fuel trim biasing. Fuel trim biasing is the time the ECM will hold a rich or lean fuel control command designed to maintain a target sensor voltage of near 600 mV.

The HO2S-2 sensor 2 is a four-wire sensor; two are used for the heater and the other two are used for the oxygen sensor signal. The HO2S-2 is an electrical source that responds to oxygen content out of the pre-catalytic converter. When the sensor reaches approximately 316°C (600°F), it produces a voltage based on the difference in oxygen between the atmosphere and exhaust gas out of the pre-converter. The ECM sends a bias voltage (450 mV) on the signal line, which can be read on the Scan tool when the sensor is cold. When the HO2S-2 is cold, it produces no voltage and has extremely high internal resistance. However, when the sensor heats up, it produces voltage that overrides the bias voltage. Normal sensor readings at steady cruise with a properly functioning catalytic converter will be steady around 500-800 mV with a target of 600 mV.