Note. For circuit reference, see WIRING DIAGRAMS article.
Circuit Description
In order to control emissions of Hydrocarbons (HC), Carbon Monoxide (CO) and Oxides of Nitrogen (NOx), a Three-Way Catalytic (TWC) converter is used. Catalyst within converter promotes a chemical reaction that oxidizes HC and CO present in exhaust gases. Oxidation process converts HC and CO into harmless water vapor and Carbon Dioxide (CO 2 ). Catalyst also reduces NOx by converting it to nitrogen. PCM monitors this process using HO2S No. 1 and No. 2. PCM compares difference between the 2 readings to determine oxygen storage capacity of the catalyst.