P0440 Code

I have a 2002 Pre-runner and i replaced gas cap and that worked for a couple of days then check engine light came on again.

I had the same problem on my 2002 it was the "Rollover Valve" on top of the gas tank, Raised the bed replaced valve, replaced bed and on we go...
I think the valve was like around $100.00 but i really don't remember. Has it already been fixed??? Was that the problem??? Please advise..