Oxygen Sensor: Description and Operation

DESCRIPTION
The Heated Oxygen Sensor (HO2S) is mounted in the exhaust system where it can monitor the Oxygen (02) content of the exhaust gas stream. The 02 content in the exhaust reacts with the sensor to produce a voltage output. This voltage ranges from approximately 0.10 volt (high 02-lean mixture) to 0.90 volt (low 02-rich mixture). This voltage can be measured with a digital voltmeter having at least 10 megohms input impedance. Use of standard shop type voltmeters will result in very inaccurate readings.

OPERATION
By monitoring the voltage output of the HO2S, the ECM will know what fuel mixture command to give to the injector (lean mixture-low O2 voltage rich command, rich mixture-high 02 voltage = lean command).

The HO2S circuit, if open, should set a DTC 13. A constant low voltage in the sensor circuit should set a DTC 44. While a constant high voltage in the circuit should set a DTC 45. DTC(s) 44 and 45 could also be set as a result of fuel system problems. See DTC charts for conditions that can cause a lean or rich system.

The HO2S works in the same manner as the non-HO2S The exception is that battery positive voltage is supplied to a heating unit that is part of the sensor itself. This heater receives voltage from the ECM's main relay circuit.

The heater helps to heat up the HO2S so the ECM can start controlling the fuel injection sooner for better fuel emissions. There are no malfunction DTC(s) to detect if the heater part of the sensor is working. To check the heater, refer to System Diagnosis / Diagnostic Charts / C-1F Heated Oxygen Sensor (HO2S) Heater Check. Testing and Inspection