I have a 2002 Camaro Z28. My ODB2 reader is putting out 2 codes PO420 and PO420 both are catalyst system efficiency and have the same definition but how different are they?

Answer 1

p0420 and p0420 are the same.

It is possible that the code is registering twice, one for each converter if you have 2.

In some cases replacing the O2 sensors helps but it is a hit and miss with these codes and most times the code comes back after a while.

The typical response to this code is to replace the converter(s). The catalyic converter is covered by an eight-year, 80,000 mile federally-mandated warranty , so dealers usually just replace it. If you're outside the warranty limits you're in a pickle, OEM cats cost over $1,000.

this code is common on cars that do a lot of in city driving. The catalytic converter hardly gets hot enough to burn off the hydrocarbons. A long highway drive may burn off enough of the contaminants on the catalyst element that it may work well enough to turn off the light.

It may take several engine start/engine stop drive cycles before the light will turn off.