Need CEL gone

I installed the doug thorley y pipe a few months ago and my check engine light has been on since. I'm going to be trading my truck in soon and would like to get it turned off before then. Any Ideas?

 

clear the system by disconnecting the battery and see if it reappears. if it continues to light up then take it to a shop that has a code reader and see what code the CEL is throwing...or buy one. comes in handy in times like this

 

Did you put back in the rear O2 sensors? If you didn't that would be a reason why your having a CEL since you've put them on.

I don't have Doug Thorley y-pipe, instead I have URD's y-pipe, you'll need the O2 simulator (from URD) since the y-pipe gets rid of your cats

Another option would be if you still have the stock y-pipe just switch it back and the CEL should dissapear