A quick tip for anyone trying to fix a p0456 DTC on an 02 Lancer. I found a cracked check valve attached to the top rear of the gas tank. I was able to remove the check valve without having to drop the fuel tank by loosening the 2 bolts that hold up the front of the tank and removing the 3 bolts from the rear, then by using a mirror I was able remove the check valve. It was cracked at the point where it attaches to the tank. First confirm that the leak is there by removing the 2 bottom hoses on the front of the EVAP canister, plug the larger hose and blow into the smaller hose, you should hear the leak above the gas tank. Exopy work fine to plug the crack on the check valve.