Oxygen Sensor: Description and Operation

Purpose:
The exhaust oxygen sensor (02S) is mounted in the exhaust system where it can monitor the oxygen content of the exhaust gas stream.

Operation:
An oxygen sensor acts as an electrochemical cell, or battery, to produce a voltage in response to the oxygen content in the exhaust stream compared to the oxygen content of the atmosphere. A lean mixture (high content in the exhaust) will produce a low voltage and a rich mixture (low oxygen content in the exhaust) will produce a high voltage. The oxygen content in the exhaust reacts with the oxygen to produce a voltage output. This voltage ranges from approximately 100 millivolts (0.1 volts) (high-oxygen lean mixture) to 0 millivolts (0 volts) (low oxygen-rich mixture).

The oxygen sensor operates between 275°C (527°F) to 850°C (1562°F).

By monitoring the voltage output of the oxygen sensor, the PCM will know what fuel mixture command to give to the injector (lean mixture-low voltage-lean command).

The oxygen sensor ground is located on the back of the engine block.

NOTE: A DTC 44 or 45 usually indicates a rich or lean engine operation, rather than a defective oxygen sensor or circuit. Therefore, it is important that the Fuel System Check be used to diagnose these codes.