Have a 96 4x4 with 2.7L engine. Just replaced a cracked exaust manafold with a newer design (welded steel instead of the cast iorn version) Now getting a check engine light code 0420 Catalytic Converter flow. Took to local mufler shop thinking it needed replaced since all of the exaust is going to it again and it looks brand new, no clogging at all. There are two sensors, 1 in front and one behind the converter. Do I need to replace both or start with one. They are about 100 bucks each at Advance and thats a Denso. Thanks for the input anyone.