Catalyst Monitor Heated Oxygen Sensors (HO2S)

In order to control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides Of Nitrogen (NOx), the system uses a three-way catalytic converter, 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 control module has the ability to monitor this process using the Heated Oxygen Sensors (HO2S). The HO2S produces an output signal which indicates the oxygen storage capacity of the catalyst, this in turn indicates the catalyst's ability to convert exhaust gases efficiently. If the catalyst is operating efficiently, the O2S signal will be far more active than that produced by the HO2S.