P0456 EVAP Leak Monitor Small Leak Detected. Tighten the gas cap, then see if the light goes off. If not, there is a small leak in the fuel vapor recovery system. That is almost impossible to find without a smoke machine. They emit a non-toxic white smoke at 2 psi that is injected into the system, then you look for where that smoke comes out. Could be a leaking hose, leaking valve, or loose hose clamp among other things.