Note. For circuit reference, see WIRING DIAGRAMS article.
Circuit Description
DTC P0420 monitors operation of bank 1 warm-up catalytic converter. DTC P0430 checks operation of bank 2 warm-up catalytic converter. In order to control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), a three-way catalytic (TWC) converter is used. The catalyst within the converter promotes a chemical reaction that oxidizes the HC and the CO that is present in the exhaust gases. The oxidation process converts the HC and CO into harmless water vapor and carbon dioxide. The catalyst also reduces NOx by converting NOx to nitrogen. The PCM has the ability to monitor this process using the fuel control HO2S and catalyst monitoring HO2S. The fuel control HO2S produces an output signal which indicates the amount of oxygen present in exhaust gases entering the TWC converter. The catalyst monitor HO2S produces an output signal that indicates the oxygen storage capacity of the catalyst in the TWC converter. The oxygen storage capacity of the catalyst is an indicator of the converter's ability to convert exhaust gases efficiently. The fuel control HO2S output signal will be far more active than the catalyst monitor HO2S output signal when the converter catalyst is operating efficiently. DTC P0420 or DTC P0430 will set if PCM detects a level of catalyst monitor HO2S activity that indicates the catalyst is no longer operating effectively.