I only go on the highway maybe once a month. But when i do, the speed limit is 65 mph. By about 5-10 minutes of driving this speed i will get a check engine light, with code P0457. I know it is a generic gas cap loose/off code. I will continue to drive until i get to my destination, plug my OBD reader in and clear the code, and also take off and re-tighten my gas cap.
It is a brand new Subaru gas cap, i purchased it because i thought it was my Stant cap leaking. Yes when i tighten it, i make sure i hear a few clicks.
Could this be another type of leak in the emission system somewhere else and the car is just reading it as the gas cap. Charcoal box have anything to do with it? Any other suggestions to fix my problem?