My 05 Silverado check enging light went out when I replaced the gas cap. It came back on after 2 tanks of gas and won't go out now. Advance Auto Parts read the code and it still is still saying it is a bad gas cap. They replaced the new cap but the light is still on. What else could it be? I don't know exactly what the code read but they said something about a bad solenoid which they said meant gas cap.