Ok there is a bulletin on this issue.
ENHANCED EVAPORATIVE EMISSION
CONTROL DIAGNOSIS AND REPAIR FOR P0446
ModelXG300/350, 2.4L SONATA
Diagnostic trouble code P0446 (Scanner Description: EVAP System: Vent Control)
sets when the fuel tank pressure sensor measures excessive vacuum in the fuel tank.
P0446 is NOT related to a system leak. The Hi-Scan EVAP LEAK CHECK will NOT
check for a P0446.
NORMAL SYSTEM OPERATION:
In an evaporative emissions system, fuel vapors and air in the charcoal canister are
drawn into the intake manifold through the canister purge valve. The vapor/air drawn
from the charcoal canister is replenished by fresh air being drawn through the EVAP air
filter and canister close valve. Normally, there is a small but measurable amount of
vacuum at the differential pressure sensor during purging.
During the system leak check (the vehicle must be driving at a steady speed over 1800
RPM), the canister close valve shuts and purging occurs until the system is drawn to
1.8 volts (measured at the differential pressure sensor). The vacuum will remain at 1.8
volts for up to 30 seconds (depending on the fuel level). This is NORMAL operation,
and should not be confused with the diagnostic procedures described later.
In a system that sets P0446, the amount of vapors being purged from the canister is
greater than the volume of fresh air entering into the canister. This causes the canister
to build up vacuum. When the canister increases in vacuum, the remainder of the
system (fuel tank, hoses, separator, etc.) will also increase in vacuum. The fuel tank
pressure sensor measures and reports the vacuum level (in volts) to the ECM. If the
vacuum level reaches beyond the ECM threshold, P0446 is set into ECM memory. If
this condition occurs on two consecutive drive cycles, then the "Check Engine" light will
Evaporative Emission Components:
1. Canister Close Valve (CCV)
6. Charcoal Canister
5. CCV Air Filter
4. Fuel Cut Valve
3. Canister Purge Valve
2. Differential Pressure Sensor (DPS)
Most common is the canister close valve need to have an evap test to diagnose this correctly .This will also cause the misfire code.This is what needs to be checked next.Hoped this helped.Positive feedback and bonuses greatly appreciated.