Oxygen Sensor: Description and Operation

(HO2S) Graph.:

PURPOSE
The (two) Heated Oxygen Sensors (HO2S), (one mounted in each exhaust manifold), monitor the amount of oxygen in the exhaust gas and convert the changes of oxygen content in to a fluctuating voltage signal.

OPERATION
The differences in oxygen content between the exhaust gas and the atmosphere make the sensors generate a voltage signal.

- A richer A/F mixture equals higher voltage (Approximately. 1 volt).
- A leaner A/F mixture equals a lower voltage (Approximately 0.1 volt).

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

Heated Oxygen Sensor (HO2S):

CONSTRUCTION
Each 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. Each sensor is equipped with an internal electric heater to help the sensors to reach operating temperature quickly. The heating element is incorporated inside the sensor housings. The heaters enable the sensors 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.

NOTE: A Diagnostic Trouble Code (DTC) will be stored for either HO2S if a failure in their respective circuits is detected by the ECM.

- DTC No. 33, Left Bank Heated Oxygen Sensor.
- DTC No. 53, Right Bank Heated Oxygen Sensor.