Fuel Control HO2S

Heated Oxygen Sensor (HO2S) Cutaway:

OPERATION
In order to control the emissions of Hydrocarbons (HC), 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 HC 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 by 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 ability of the catalyst to convert the 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 HO2S sensors which are used in order to monitor the catalyst function are the same as the HO2S sensors which are used in order to control the fuel. Bank 1 Sensor 2 and Bank 1 Sensor 3 are used primarily for catalyst monitoring. These sensors 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 the fuel trim in order to ensure that the fuel delivery is correct for catalyst monitoring.