I have a 04 and my check fuel cap light has been coming on for a while now every time I turn on my truck. I calley the dealership and they said I needed to change the fuel cap which I did. The code still comes on wverytime i turn on the truck. A few ago the Check Engine light came on so I took it to Auto zone they said it was code P0193 Fuel Rail Pressure sensor. How do I know for sure what the problem is before I spend to much money or take it to the wrong place? If anyone know please send help my way.