P0446 code on a 2004 ford expedition 5.4 - 2004 Ford Expedition

P0446 - Evaporative Emission Control System Vent Control Circuit Malfunction

Evap vent valve has only one purpose. It closes in order to seal the vent so the EVAP system can pressurize and ensure there are no leaks. Evap vent valve is usually supplied Batt. voltage with key on. The ECM's driver controls the ground, and when grounded, activates the valve (closing it). If the ECM detects a short to ground, and open,or a short to battery voltage on the control circuit, P0446 will set. Code also may refer to ECM detecting that EVAP system is unable to achieve or maintain vacuum during test.

Symptoms: There will be no obvious symptoms to driver, other than MIL illumination.

Causes: A code P0446 could mean one or more of the following has happened:
* Faulty vent valve
* Open, short or excessive resistance on Vent valve control circuit
* Blockage of vent valve
* Bad PCM

Possible Solutions: With a P0446 OBD-II trouble code, here are some things to try:
* Replace Vent valve
* Repair open, short, or resistance problem in control circuit
* Repair open, or short, or resistance problem in power circuit
* Replace PCM

I hope help with this (remember to rate and comment this).

That is an EVAP code. WHat that means is you evaporative emission system showed a fault long enought to set a diagnostic trouble code. A majority of the time this code is set because a fuel cap was not properly seated after fueling the vehicle. Did this code set shortly after adding fuel to the vehicle?
It isn't as common but the code can also be set by other components of the EVAP system including the fuel cap itself, the EVAP Purge Valve, Fuel Tank Pressure sensor, A leak somewhere in the EVAP System plumbing, or even the Powertrain Control Module (computer). However, the first thing to check and the most likely culprit if the fuel filler cap.