Engine light stays on

1684 means the battery was recently disconnected.

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.