Had the SES light come on a few weeks back and following the instructions posted by "TYLER-Canada" and simplified by Grip, found PO456 "slight leak at gas cap" fault. The timing re finding the code and resetting the SES very precise...took me several attempts...do a search re SES and read thread "resetting SES light"
My SES came on within the first 3000 miles of owning my new Murano. It was reset once by the dealer and came on again. The first time, the code read "very small leak" and was attributed to gas tank filler cap having a faulty seal. The second time, another dealer did a complete evap leak test and noted a small leak at the front side of the engine. The hoses were tightened, the code reset and the problem has not re-occurred.
If your first reset works and keeping the gas cap on tightly prevents the reoccurance of the SES light, you're all set. If not, make sure your dealer service technician checks the gas cap seal AND runs a full evap leak test.