Rear Heated Oxygen Sensor

The rear heated oxygen sensor is placed into the front exhaust tube. It detects the amount of oxygen in the exhaust gas compared to the outside air. The rear heated oxygen sensor has a closed-end tube made of ceramic zirconia. The zirconia generates voltage from approximately 1V in richer conditions to 0V in leaner conditions. The rear heated oxygen sensor signal is sent to the ECM. The ECM adjusts the injection pulse duration to achieve the ideal air- fuel ratio. The ideal air-fuel ratio occurs near the radical change from 1V to 0V.
Under normal conditions the rear heated oxygen sensor is not used for engine control operation.