Oxygen Sensor: Description and Operation

Heated Oxygen Sensor (HO2S) Cutaway:

OPERATION
To control emissions of Hydrocarbons (HO), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), a three-way catalytic converter is used. The catalyst within the converter promotes a chemical reaction which oxidizes the HO and CO present in the exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen. The VCM has the ability to monitor this process using the Bank 1 Sensor 2 and the Bank 1 Sensor 3 heated oxygen sensors. The Bank 1 Sensor 2 sensor produces an output signal which indicates the amount of oxygen present in the exhaust gas entering the three way catalytic converter. The Bank 1 Sensor 3 sensor produces an output signal which indicates the oxygen storage capacity of the catalyst; this in turn indicates the catalyst ability to convert exhaust gases efficiently. If the catalyst is operating efficiently, the Bank 1 Sensor 2 sensor will produce a far more active signal than that produced by the Bank 1 Sensor 3 sensor.

The catalyst monitor sensors operate the same as the fuel control sensors. Although the Bank 1 Sensor 2 and Bank 1 Sensor 3 sensors main function is catalyst monitoring, they also play a limited role in fuel control. If a sensor output indicates a voltage either above or below the 450 millivolt bias voltage for an extended period of time, the VCM will make a slight adjustment to fuel trim to ensure that fuel delivery is correct for catalyst monitoring.

Refer to System Diagnosis / Diagnostic Charts for testing information. Testing and Inspection