So my truck has been telling me to check my gas cap. I find this a little odd but I check it take it off then put it on truck still tells me to check it! Is there a sensor in gas caps? I find this a little weird but it is causing my check engine light to come on as well. Any Ideas or should I just replace my gas cap?

 

Nope, it (the system) senses that there's a leak. (not leaking gas externally, just atmospheric leak as in a broken or bad seal on the cap). If you have a buddy that has the same truck borrow his cap for a moment to try it. If the light goes off, you know you need a new cap. Probably just a cracked or leaky seal. It may not necessarily LOOK bad, but "the check engine light knows if it's bad". If a cap isn't too expensive, I'd just replace it. I put a locking cap on mine when I bought it. I don't think it cost more than $12.-$14. at the parts store for a Stant locking cap.

(No sensor IN the cap)

 

The cel is probably reporting a gross leak in the evap system, that is if your gas cap isn't at fault.

If you have a cel other than "gas cap" get it read and post it up here.