NancysToy
Motorbike Professor
The procedure in the manual is to disconnect the electrical connector for the purge valve and then hot-wire it and listen for it to open and close. I've done that (carefully so you don't short anything out -- if you have heavy fumes I'd be careful of the spark) and it makes a loud, audible click. That's no guarantee it's opening or closing 100% but at least that it's working. Then I believe there's a second procedure involving BUDS which checks if the computer is telling it to open at the right time. Even though mine checked out OK on hot-wiring and the dealer said OK on BUDS, in frustration I replaced the valve and canister. Didn't make any difference. I have a 2011 so the problem is not as bad as you describe but I'm not happy, either. For fun, I cut the old canister apart and it was perfect inside -- full of nice, dry activated charcoal. So I'm stymied right now, too.
If I remember correctly, there is also a vacuum test for leakage. If not, there should be. That would be aimed more at performance problems however, not the failure to adequately evacuate the canister.