Oxygen Sensor: Description and Operation

Exhaust Oxygen Sensor (02):

PURPOSE
The Oxygen Sensor (O2S) is mounted in the exhaust system where it can monitor the oxygen content in the exhaust gas stream.
By monitoring the voltage output of the O2S, the Powertrain Control Module (PCM) will know what fuel mixture command to give to the injectors.

(lean mixture-low O2S voltage = rich command
rich mixture-high O2S voltage = lean command)

OPERATION
The oxygen content in the exhaust reacts with the sensor to produce a voltage output. This voltage ranges from approximately 0.1 volt (high oxygen content - lean mixture) to 0.9 volt (low oxygen content - rich mixture). This voltage can be measured with a digital voltmeter having at least 10 megohms input impedance. Use of a standard shop type voltmeter will result in inaccurate readings.

The O2S, if open, should set a Diagnostic Trouble Code (DTC) 13. A constant low voltage in the sensor circuit should set a DTC 44. A constant high voltage in the circuit will set a DTC 45. DTCs 44 and 45 could also be set as a result of fuel system problems.