Heated Oxygen Sensor (HO2S)



The heated oxygen sensor detects the amount of oxygen in the exhaust gas compared to the outside air. The front heated oxygen sensor (left bank) has a closed-end tube made of ceramic zirconia. The zirconia generates voltage from approximately one volt in richer conditions to zero volts in leaner conditions. The front heated oxygen sensor (left bank) signal is sent to the ECM. The ECM adjusts the injection pulse duration to achieve the ideal air/fuel ratio, which occurs near the radical change from one to zero volts.

Click image to see an enlarged view

Fig. The heated oxygen sensor (left bank shown)


  1. Check the resistance between terminals 3 and 1. Resistance should be 2.3-4.3 ohms at 77°F.
  3. Check if there is any continuity between terminals 2 and 1 and 3 and 2. No continuity should exist.
  5. If either of these checks have failed, replace the front heated oxygen sensor.
    Discard any heated oxygen sensor which has been dropped from a height of more than 20 inches onto a hard surface, such as a concrete floor, and use a new one.