DTC P0420: Catalyst System Efficiency Below Threshold - Bank 1 Or DTC P0430: Catalyst System Efficiency Below Threshold - Bank 2: Description
WARNING: This page is about a different car, the 2002 Nissan Xterra and 2002 Nissan Frontier. However, it is still accessible from the selected car via links, so may be relevant.
The ECM monitors the switching frequency ratio of HO2S1 and HO2S2. A 3-way catalyst with high oxygen storage capacity will indicate a low switching frequency of HO2S2. As oxygen storage capacity decreases, HO2S2 switching frequency will increase. When the frequency ratio of HO2S1 and HO2S2 approaches a specified limit value, the 3-way catalyst malfunction is diagnosed.