Since it's a 06 do you still have the warranty? If so i'd bring it to the stealership to get checked.

Have you had any issues with the car before?, did you get a carfax on the car when you bought it to see if it was in any accidents?

Just tryin to dig a lil deeper for a solution!!!

 

I had the "tighten gas cap"come up before.. What my problem was is that the cap's gasket was actually going bad so it wasn't making a complete seal.. Had the dealership replace the cap with a new one since it was still under the warranty.