HO2S Bank 1 Sensor 2 and HO2S Bank 2 Sensor 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 per bank. Fuel trim biasing is the time the ECM will hold a rich or lean fuel control command designed to maintain a target heated oxygen sensor 2 signal voltage of near 600 mV.

The heated oxygen sensor 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. At this temperature, the sensor is fully functional. 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 heated oxygen sensor 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.

Each heated oxygen sensor 2 contains a heater element controlled by the ECM necessary to speed up fuel trim bias activation. The ECM will pulse the heater until it has determined exhaust pipe moisture has evaporated (engine run time between 0 and 200 seconds). After that, the ECM will command the heater On at a 100% duty cycle for 10 seconds, after which it will turn Off the heater for a very short amount of time to test for an open/low voltage condition. The ECM will continue to do this unless the exhaust gas temperature exceeds 850°C (1562°F). The heater will be pulsed if this limit is exceeded.