Heated Oxygen Sensor 1 (HO2S-1)

Heated Oxygen Sensor 1 (HO2S-1):

The HO2S-1 is located in the exhaust manifold used by the PCM to make fuel control corrections toward a 14.7 to 1 air/fuel ratio. The sensor is a four wire sensor. Two circuits are used for the heater and the other two are used for the oxygen sensor signal. The HO2S-1 is an electrical source that responds to oxygen content in the exhaust manifold. 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. The PCM sends a bias voltage (399-499 mV) on the signal line, which can be read on the Scan tool when the sensor is cold. When the HO2S-1 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. This voltage is read by the PCM to determine a rich/lean HO2S-1 signal used to adjust injector pulse width. Under normal conditions, low sensor voltage means high oxygen content/lean air-fuel mixture and vice versa. Normal sensor readings will fluctuate between 10 mV and 1065 mV.