Check engine code

I have a 2007 4l V6. The check engine light came on and I scanned it and got : "P0455 generic evaporative emission system leak gross leak/no flow". Is anyone familiar with this issue? Suggestions welcome.

 

Easy first step would be check the gas cap.
There is a big o-ring on the cap. Check to see if it is damaged.

Also, make sure the cap is on tight.

Now, that being said.
The gas cap on the 2nd Gen trucks only turn so far.
The threads are not continuous in the cap.
It reaches a point and stops. You CAN NOT physically make the cap get tighter once it hits that stop.
Which is even more of a rwason to check the cap and o-ring.

 

I had same code plus a couple more having to do with evap. Changed solenoid, gas cap, charcoal canister filter. Has to replace charcoal canister with doorman CELs been off since with no pending codes.