So I just got a Fullrace 3" catless downpipe installed on my 2013 civic si coupe. Now I know since its catless that it will throw a CEL and to my knowledge if you use a flashpro to disable the "P0420 catalytic efficiency error" then the CEL should go away , right? Well I did that and when I first cranked up the car it showed no CEL, I even ran an OBDII diagnostic with flashpro and everything seemed to be in order. However when I started the car up for a second time it showed a CEL and upon running another OBDII diagnostic it was caused by the feature that I had diabled. I'm new to modifying cars but I try to do my research and I cant figure it out. Thanks in advance, if you need more info just ask.