Code P0420 means "Catalyst System Efficency Below Threshold (Bank 1)" P0420 is actually Catalyst System Efficiency Below ThresholdCatalyst System Efficiency Below Threshold.
Bank 1 is the side of the engine with cylinder #1. This code means that the catalytic converter is not cleaning the exhaust properly or the oxygen sensors are sending false info to the computer.
Trouble code P0420 means: Catalyst Efficiency Below Normal (Bank 1)
Trouble code P0420 means: Catalyst System Efficiency Below Threshold (Bank 1)
Trouble code P0420 means: Catalyst System Efficiency Below Threshold (Bank 1)
Trouble code P0420 means: Catalyst Efficiency Below Normal (Bank 1)
Trouble code P0420 means: Catalyst Efficiency Below Threshold (Bank 1)
Trouble code P0420 means: Catalyst Efficiency Below Normal (Bank 1)
P0420 Catalyst System Efficiency Below Threshold (Bank 1)
Trouble code P0420 means: Catalyst System Efficiency Below Threshold (Bank 1)
Trouble code P0420 means: Catalyst Efficiency Below Threshold (Bank 1)
Trouble code P0420 means: Catalyst Efficiency Below Threshold (Bank 1)
Trouble code P0420 means: Catalyst system efficiency below threshold (bank 1)
Trouble code P0420 means: Catalyst Efficiency Below Normal (Bank 1)