DTC P0420 & P0430: TWC System - Low Efficiency - Bank 1 & 2: Description

WARNING: This page is about a different car, the 2002 Pontiac Firebird and 2002 Chevrolet Camaro. However, it is still accessible from the selected car via links, so may be relevant.

In order to maintain reasonably low emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx), the engine controls system uses a 3-way catalytic converter. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO in the exhaust gas. This reaction converts these chemicals into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting the NOx to nitrogen. The Powertrain Control Module (PCM) monitors this process using Bank 1 HO2S #2. Bank 1 HO2S #2, located in the exhaust stream past the 3-way catalytic converter, produces an output signal which indicates the oxygen storage capacity of the catalyst. This determines the catalyst's ability to effectively convert the exhaust emissions. If the catalyst is functioning correctly, the Bank 1 HO2S #2 signal will be far less active than the signal produced by Bank 1 HO2S #1. This indicates that the 3-way catalytic converters oxygen storage capacity is below an acceptable threshold. When the Conditions for Running this DTC are met, the following conditions occur:

The PCM captures the current rear HO2S rich-to-lean status.
The Air/Fuel ratio transitions from rich to lean, or from lean to rich, depending on the capture rear HO2S rich-to-lean status.
The Air/Fuel ratio transitions a second time opposite the first Air/Fuel ratio transition.
The PCM captures the response time of the front and rear heated oxygen sensors when the Air/Fuel ratio transitions occurred. The response time is the time during which the HO2S goes from below 300 mV to above 600 mV, and from 600 mV to below 300 mV.
The PCM measures the time for the rear HO2S voltage to cross a reference rich-to-lean threshold, minus the time for the front HO2S voltage to cross the same rich-to-lean threshold. The time difference from the front and rear HO2S is the oxygen storage capacity of the catalyst. This DTC sets if the time exceeds a predetermined threshold.