Oxygen (O2) Sensor
The sensors are mounted in exhaust system where they can monitor oxygen content of exhaust gas stream. See Fig 1 . An oxygen sensor acts as an electrochemical cell, or battery, to produce a voltage 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 and a rich mixture (low O2 content in exhaust) will produce a high voltage. The oxygen content in exhaust reacts with oxygen sensor to produce a voltage output. This 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, ECM will know what fuel mixture command to give to injector (lean mixture/low voltage/rich command; rich mixture/high voltage/lean command).
The ECM controls left (front) bank of injectors separately from right (rear) bank of injectors. The left (front) O2 sensor is used for left bank fueling and will set a Code E017 if sensor circuit is open. The left O2 sensor will also detect lean or rich fueling problems and set Code E042 or E043.
The right (rear) O2 sensor is used by ECM for right bank fueling and will set a Code E013 if sensor circuit is open. The rear O2 sensor will also detect lean or rich fueling problems and set Code E044 or E045.
The engine will run in "Open Loop" mode only if there is a problem detected on both oxygen sensor circuits.