it's a crap shoot unless you take it to your auto parts store for a free code read. mine was the gas cap not on tight (3 clicks) and this time around, the flapper valve was sticking on my evap canister ($60) part.
If the code comes up P0455 , then it either the gas cap, or the purge valve from the
Had it come up 5-6 times on my 05 ( and the cap was fine ) , so did the upgrade on the
purge valve per Nissan TSB and parts, no issues since. Not cheap but fixed it .
The filler neck threads get dry and makes the cap click to early before its tight. Take and wipe alittle grease on the threads and work the cap on and off a few times and you'l feel the the cap get tighter.I've fixed many like this.