I'd try a new Original Equipment fuel filler cap first

https://www.autocodes.com/p0446_ford.html

I agree with @glen_stet here. The gas cap is the "low hanging fruit". What's happening is the computer is testing the EVAP system. 

It commands the EVAP Canister Vent Valve to Close (that's not normal but it does it specifically for this test). It commands the Evap Canister Purge valve to Open and the engine intake manifold vacuum caused by the EVAP Canister Purge Valve being Opened and the Evap Canister Vent Valve being Closed pulls negative pressure on the fuel tank.

Then the computer closes the Purge Valve and it uses the Fuel Tank Pressure Sensor to measure the rate of negative pressure deterioration with the system sealed up.

If it isn't holding negative pressure the computer typically blames the Vent Valve (P0446).

But a faulty gas cap, a faulty vent valve, or a faulty fuel tank pressure sensor can set that code.