My check emissions light came on so my first stop was to AutoZone. They hooked me up and they gave me the P0171 code. Now my truck runs fine, no hesitation, no rough idle or anything. Could this become something major? Thanks!

 

I think that's a lean code. Check for vacuum leaks and look around your intake for anything out of the ordinary to start.

 

Mine was throwing that a little while back. Turned out to be my vacuum hoses. A little while later I had to replace two coil packs.