Hello, the other day my check engine light came on, read code P0440 Evap Emission control malfunction. I had the light turned off but it came back on today, I am assuming its the same code (will read the code tomorrow for sure). Now I did a little research on this and understand that it could be the gas cap, Purge solenoid, purge valve or plugged system. Which system is the best one to go after first? Ie how do I test the purge solenoid or purge valve? I am a student at a tech school so I am trying to diagnose this myself to save money but do not want to go changing parts at random. Any help would be appreciated. Thanks.