how to diagnoise a po455 on my 2006 pontiac g6 3.5 engine? on 2005 Pontiac G6

I have change the gas cap with an oem piece,check the fill neck and tube and it looks ok and i have tried the drive cycle test to see if the monitors would be ready so i can go for my inspection sticker and pass the emissions test.How can i go further to diag my PO455 code?

Asked by for the 2005 Pontiac G6
you need a smoke mach to go can also test all evap components. see your mech and save time and $.