Oxygen Sensor: Description and Operation

Oxygen Sensors:

PURPOSE
Two Heated Oxygen Sensor (HO2S) are mounted in the exhaust system where they monitor the oxygen content in the exhaust stream. There is an oxygen sensor mounted in each exhaust manifold.

OPERATION
An oxygen sensor acts like a battery because it creates its own signal voltage once it reaches operating temperature. This voltage is produced when the oxygen content in the exhaust stream is different than the oxygen content in the atmosphere. A lean condition (high oxygen content in exhaust) will produce a low voltage (near 0 volt) and a rich condition (low oxygen content in exhaust) will produce a high voltage (near one volt). The PCM provides a reference signal voltage (0.45 volt) and a ground to the sensor. The PCM reference voltage is necessary because the oxygen sensors do not provide their own voltage until they reach operating temperature.

The PCM uses oxygen sensor information during 'Closed Loop' operation to constantly adjust fuel control to reduce exhaust emissions. Because the oxygen sensors provide information sooner after engine start-up, exhaust emissions are reduced. Faulty oxygen sensors will cause various driveability conditions and should set a Diagnostic Trouble Code.

CONSTRUCTION
The oxygen sensors also incorporate a heating element inside of the sensor housing. This heating element is energized with the ignition 'ON' and allows the sensors to reach operating temperatures quickly. The PCM can then use oxygen sensor information sooner after engine start-up.