Well if it is anything like the charcoal canister system Toyota uses on the early Yaris, you'll have the same frustrations as I had. The charcoal canister/valve assembly fails due to water entry. Toyota somehow has gotten around the canister being included in the extended emissions warranty. Dealers will not warranty the repair. Although I do not see how ARB and EPA have not seen enough failure reports to mandate action, especially since Toyota issued a TSB acknowledging the failure. I wonder if the same was done for the other Toyota models?
In my case it was a $850 part plus labor to install or a $550 part that I could self-install. Can you guess which way I chose? After a new canister, filter assembly, vapor collar, and a weekend afternoon it was done. It's only a matter of time before it occurs again since its the same designed parts (I hope to get ride of it before that happens). I hope our new Rav does not experience the same thing.....
Best of luck to you.
PS. Speaking of the canister solenoid (valve), be cautious if you follow the FSM troubleshooting procedure. It has you remove the solenoid from the canister at one point to check operation. The solenoid is bolted to the canister via threaded inserts into the plastic housing which are certain to strip the bond to the housing since there will be some thread corrosion working against you = instant buying a new canister.