The exhaust oxygen sensor is mounted in the exhaust system where it can monitor the oxygen content of the exhaust gas stream. The oxygen content in the exhaust reacts with the oxygen sensor to produce a voltage output. This voltage ranges from approximately 100 millivolts (high oxygen-lean mixture) to 900 millivolts (low oxygen-rich mixture).
By monitoring the voltage output of the oxygen sensor, the ecm will determine what fuel mixture command to give to the injector (lean mixture-low voltage-rich command, rich mixture-high voltage-lean command).
Remember that oxygen sensor indicates to the ecm what is happening in the exhaust. It does not cause things to happen. It is a type of gauge: high oxygen content = lean mixture; low oxygen content = rich mixture. The ecm adjust fuel to keep the system working.
The oxygen sensor, if open should set a Code 13. a constant low voltage in the sensor circuit should set a Code 44 while a constant high voltage in the circuit should set a Code 45. Codes 44 and 45 could also be set as a result of fuel system problems.Precautions: