Oxygen Sensor (O2S 1)

The Oxygen Sensor (O2S 1) 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 sensor to produce a voltage output. This voltage ranges from approximately 0.1 volt (high oxygen-lean mixture) to 0.9 volt (low oxygen-rich mixture). This voltage can be measured with a scan tool.

By monitoring the voltage output of the O2S 1, the PCM will know what fuel mixture command to give to the injectors.
^ Lean mixture-low O2S 1 voltage = rich command
^ Rich mixture-high O2S 1 voltage = lean command

The O2S 1, if open, should set a DTC P0134. A constant low voltage in the sensor circuit should set a DTC P0131. A constant high voltage in the circuit should set a DTC P0132. DTCs P0131 and P0132 could also be set as a result of fuel system problems. See the DTC tables for conditions that can cause a lean or rich system.