Hi pls help me out guys. I have been chasing this CEL for some time now. First it threw a front o2 sensor-replaced it. Then it threw a rear o2 sensor-replaced it. then Now a Po420. Its driving me nuts. There is no misfire. cylinder head gasket was replaced 4k miles ago. light came on 2k miles ago. Just replaced with OE parts- spark plugs, fuel filter, fluids, airfilter etc. engine runs fine when there is no CEL. if you have a GOOD catalytic converter laying around for a a non turbo 2.5 sohc please PM me. thanks