Hi I am kinda new on here,ive been looking at this forumn for a while now and finallly decided to register.. ive owned my msp for about half a year, I just installed a sls catless midpipe and have just thrown the p0421 trouble code. I cannot feel any difference.in my car, it seems to be running fine. I was wondering what has happened to.others after they have installed this midpipe and what did you do about it?