Check engine light

2009 check engine light comes on when my fuel level drops around half way, and nearly always goes off when I refill ???...I live in Florida, I've notice it's worse in colder weather. Had it cleared many a time but now I just live with it, the car runs fine, getting around 45 mpg but it's very annoying !!!
Anyone ?

The code check suggested a flow valve replacement, however, whats that got to do with gas fill ups that 99% solves the issue, until it drops to around half way ???