DTC P0420: Bank 1 Catalyst System Efficiency - Below Threshold Or P0430: Bank 2 Catalyst System Efficiency - Below Threshold : Description
WARNING: This page is about a different car, the 2003 Nissan Pathfinder. However, it is still accessible from the selected car via links, so may be relevant.
The ECM monitors the switching frequency ratio of HO2S 1 and HO2S 2. A warm-up 3-way catalyst with high oxygen storage capacity will indicate a low switching frequency of HO2S 2. As oxygen storage capacity decreases, HO2S 2 switching frequency will increase. When the frequency ratio of HO2S 1 and HO2S 2 approaches a specified limit value, the warm-up 3-way catalyst malfunction is diagnosed.