Oxygen (O2) Sensor
The exhaust oxygen sensor is mounted in exhaust system where it can monitor oxygen content of exhaust gas stream. See Fig 1 . The oxygen sensor acts as an electrochemical cell or battery. A voltage is produced in response to amount of oxygen in exhaust stream compared to oxygen content of atmosphere. A lean mixture (high O2 content in exhaust) will produce a low voltage. A rich mixture (low content in exhaust) will produce a high voltage. Oxygen sensor voltage ranges from approximately 100 millivolts (0.1 volts) (high O2 - lean mixture) to 900 millivolts (0.9 volts) (low O2 - rich mixture).
By monitoring voltage output of O2 sensor, PCM will know what fuel mixture command to give to injector(s) (lean mixture-low voltage-rich command; rich mixture-high voltage-lean command).
The O2 sensor, if open, should set a Code E013 or Code E017. A sensor circuit shorted to ground should set a Code E042 or Code E044. A sensor circuit shorted to voltage should set a Code E043 or Code E045. When any of these codes are set, car will run in Open Loop Mode.