Oxygen Sensor (O2S) Sensor 1

The Oxygen Sensor (O2S) sensor 1, mounted in the exhaust system, monitors the oxygen content in the exhaust gas stream. The oxygen sensor acts as an electrochemical cell, or battery, to produce a voltage in response to oxygen in the exhaust stream compared to oxygen content of the atmosphere. A lean mixture (high oxygen in the exhaust gas) produces a low voltage and a rich mixture (low oxygen content in the exhaust gas) produces a high voltage. The voltage signal ranges from approximately 100 millivolts (0.1 volt) for a lean mixture to 900 millivolts (0.9 volt) for a rich mixture.

By monitoring the voltage output of the front oxygen sensor, the PCM will vary the injector pulse width in order to control the air-fuel ratio.