Alright I've been noticing this since I got the car 2 years ago, The check engine light comes on an goes off when it wants to even when I haven't done anything to fix it.. Just recently I had the code P0440 (evap leak) this has had my check engine light on for the past few months now and I replaced the fuel cap back in January (I always make sure to install the fuel cap properly) but the light stayed on with same code.. the weird thing is just this morning I start the car no check engine light. Car still runs the same as the day before

 

There is much more to the P0440 then a gas cap. There are a few different evap leak codes and pretty much each one GM tells you to smoke test the car to locate the leak.

I would recommend re-checking the codes in the car's history and see if P0440 is still popping up.

 

Chevy kid do you leave the car running when you get gas that could do it.

 

Yea I know its just the gas cap is what everyone normally points out first when there is a evap leak so i thought i should mention it was already replaced .. about a month ago I replaced my thermostat and I accidentally ripped my purge solenoid in the process so that was replaced. But yea its looks like thats my only option smoke testing it

 

No I always shut the car off when I fill up.. but thanks for the tip ill keep that in mind

 

So the light was off when I went to work this morning and it was still off on my way back home .. I just ran the car a few minutes ago an there it goes check engine light back on.. does anyone have this same problem?