Hi I am a newbie and have a 1999 Honda Accord 2.3L ULEV. Well according to my ULEV/Carb compliment sticker and valve cover. However looking up my vin it says it's a f23A1. On the engine block it says f23A4 and even my insurance has it down as an A1. My issue is I have a 0420 code I can't clear up. I put a new downstream Denso 02 and found an air leak on my intake boot I fixed. Also bought a new Magnaflow federal approved Cat. Just hav'nt installed it yet. Any suggestions on what it could be?

 

According to the web the f23A4 takes a different O2 sensor