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 2002 Nissan Pathfinder and 2002 Infiniti QX4. 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.