The service engine soon lite came on .Took it to auto zone they said it's a PO420 code. Just put catted xpipe on slp loud mouth at deans peformance about 500 miles ago. Car ran great till now what to do. Any help would be great thanks RON there is no tune or mil elminators or pulley .the car has a jlt cold air intake slp catted xpipe and borla stingers