Gas fumes under truck but no leaks,Cap OK on 2003 Chevrolet Trailblazer

Dont know if canister or valve bad.

Asked by for the 2003 Chevrolet Trailblazer
If the canister is easily accessible I would take it off and see if it's saturated, you can usually tell right away by how much it weighs and if you can smell raw fuel in it.