DTC P0420: Catalyst System Efficiency Below Threshold: Notes
WARNING: This page is about a different car, the 2003 Acura 3.2TL and 2003 Acura 3.2CL. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
If DTCs P0137, P0138 or P0141 are also stored, troubleshoot these codes first.