What if the cap is new and is tight?

Question

I put a brand new Stant gas cap on and did get this code again P0457.

Answer 1

Check the "T" fitting and Vacuum Control Solenoid located below the intake manifold, check these two things first .Then "T" had hoses attached and the Vacuum Control Solenoid and then focuse on the Drain Valve, also called Canister Vent Valve (P/N:42084FA120)  which is known for going bad.