fuel cap check engine lights are on auto zone say its the cap but light still on

"The Evaporative Emission Control System (EVAP) is used to prevent gasoline vapors from escaping into the atmosphere from the fuel tank and fuel system. The EVAP system usually requires no maintenance, but faults can turn on the Check Engine light and prevent a vehicle from passing an OBD II plug-in emissions test." EVAP Evaporative Emission Control System - AA1Car.com