Maybe this is a little late, however I had this same "Check Gas Cap" issue, I replaced the cap and the light stayed on, I believe that was the same code, I chased a few different EVAP sensors, and then I found it, being the 'EVAP Vent Solenoid/Purge Vent Solenoid' (something along those lines) underneath the rear bumper, on the left hand side. Look under the car and straight up near the gas filler neck and you'll an odd, soda can sized plastic canister, I replaced it and cleared the code. Never came back this was on 10/02/2016 @ 192,141miles.
