DTC P0420: Catalyst System Low Efficiency: Description

The catalyst within the catalytic converter promotes a chemical reaction with oxidizes Hydrocarbons (HC) and Carbon Monoxide (CO) that is present in the exhaust gas. This reaction converts the compounds into harmless water vapor and in carbon dioxide. The catalyst will also convert the Oxides of Nitrogen (NOx) into nitrogen. Powertrain Control Module (PCM) monitors this process via the signal from Heated Oxygen Sensor (HO2S) 1. HO2S 1 produces an output signal which indicates oxygen storage capacity or the catalyst. Oxygen storage capacity is one method of determining the catalyst's ability to convert exhaust emissions effectively. If catalyst is functioning correctly, HO2S 2 will be less active than HO2S 1 sensor 1 signal. If PCM detects excess HO2S 2 signal activity for an extended period of time, Diagnostic Trouble Code (DTC) P0420 will set.