P0420 2001 Toyota Camry -

Question

I have a 420 code, replaced the cat, and still have a 420 code, engine runs fine

Answer 1

P0420 Catalytic threshold below effiency

P0420 does not always means there is a problem with the catalytic, In order for a catalytic to be functional the 02 sensor must go from rich to lean. and the 02 must cycle at a certain speed this is known as a hertz. .5 hertz to 5 hertz is the standard. Below .5 hertz the 02 sensor is degraded this in return affects fuel control and the catalytic cannot work properly.Above 5 hertz you have a misfire. Proper sparkplugs, clear air filter proper fuel pressure , all contribute to a proper fuel control management.