Ford P0420 OBD-II Trouble Code Definition: P0420 Catalyst System Efficiency Below Threshold Bank 1 P0420 Ford OBD-II Trouble CodeDescription: OBD Trouble Code P0421 Warm Up Catalyst Efficiency Below Threshold What does the code mean? OBD-ii Code P0421 definition: Basically this means that the oxygen sensor downstream of the catalytic converter on bank 1 is detecting that […]