Heated Oxygen Sensor (HO2S 1)

The Heated Oxygen Sensor (HO2S 1) is mounted in the exhaust before the catalytic converter where it can monitor the oxygen content of the exhaust gas stream.

The oxygen content in the exhaust reacts with the sensor to produce voltage output. This voltage should constantly fluctuate from approximately 100 mV (high oxygen content lean mixture) to 900 mV (low oxygen content rich mixture). The heated oxygen sensor voltage can be monitored with a Tech 1.

By monitoring the voltage output of the heated oxygen sensor, the Vehicle Control Module (VCM-A) calculates what fuel mixture command to give to the injector (lean mixture-low HO2S 1 voltage=rich command, rich mixture-high HO2S 1 voltage=lean command).

The heated oxygen sensor circuit, if open, should set a Diagnostic Trouble Code (DTC) P0134 and the Tech 1 will display a constant voltage between 350 - 550 mV. A constant voltage below 250 mV in the sensor circuit should set DTC PO131, while a constant voltage above 950 mV in the circuit should set DTC PO132. DTC P0131 and DTC P0132 could also he set as a result of fuel system problems. Refer to DTC charts for conditions that can cause a lean or rich system. Refer to Diagnostic Trouble Code Charts. Under Computer and Controls/System Diagnosis/Procedures. Testing and Inspection