I have a Evo IX and about the 800 mile mark I installed a Forge Type RS BOV and Greddy TiC Catback exhaust. At the 3,500 mile mark I got a SES light....? It was P0420 Catalyst efficiency below threshold (bank 1) What could of caused the light to come on? I spoke with Mitsubishi and they said it was a back Cat. Its not the first 06' to have that prob.

Your help and suggestions are greatly appretiated.

 

Could be a wiring issue, wouldnt be the first time that happened too.. then again, it could be a lot of other things.