Hey guys my truck's check engine light came on today. I did the click on off on off x4 while holding the odometer to check the code, and it says "CHEC" that's it...so i'm not sure what to make of that. Truck seems to be running fine so no obvious signs of anything wrong. Maybe an o2 sensor went bad but i'm not sure. This only happened after I had my magnaflow muffler put on, but I don't see how that affected anything in an adverse way. Anyone able to shed light on this? Does Napa provide a service to plug in a diagnostic code reader into your vehicle to tell you what's wrong? I was planning on finding out tommorow so I can fix it myself asap.