Oxygen Sensor: Description and Operation

Heated Oxygen Sensor:

PURPOSE
The Heated Oxygen Sensor (HO2S) monitors the amount of oxygen in the exhaust gas.

OPERATION
The differences in oxygen content between the exhaust gas and the atmosphere make the sensor generate a voltage signal.
The voltage is approximately 1 Volt in a richer condition of the mixture ratio, while approximately 0 Volts in leaner conditions. The radical change from 1 Volt to 0 Volts occurs at around the ideal mixture ratio. In this way, the Heated Oxygen Sensor detects the amount of oxygen in the exhaust gas and sends the signal of approximately 1 Volt or 0 volts to the Engine Control Module (ECM).

The ECM interprets the voltages and number of voltage "swings" (cross-counts) and will vary injector open times to control the air-fuel ratio.

To help the sensor to reach operating temperature quickly, a heating element is incorporated inside the housing. The heater enables the H02 sensor to reach operating temperature in a matter of seconds, as opposed to minutes with non-heated sensors. The advantages of a heated sensor are better driveability and lower emissions during warm-up.

CONSTRUCTION
The sensor has a closed tube made of ceramic zirconia. The inner surface of the tube is is exposed to atmosphere while the outer surface is exposed to the exhaust gas. In order to improve the generating power of the zirconia, it's tube is coated with platinum.