Yes, it is with the evap system. This indicates that a part of the EVAP control system is no longer fuctioning correctly. The P0446 code is similar in nature to the P0441 code. The EVAP system consists of many parts, including (but not limited to) the gas cap, fuel lines, carbon canister, purge valve, and other hoses. The (EVAP) emission control system prevents the escape of fuel vapors from a vehicle's fuel system. Fuel vapors are routed by hoses to a charcoal canister for storage. Later, when the engine is running a purge control valve opens allowing intake vacuum to siphon the fuel vapors into the engine.
EVAP emission canister purge is contolled by a valve which allows engine vacuum to pull stored fuel vapors from fuel tank into the engine to be burned, rather than be vented to atmosphere. A vacuum switch is used to detect when flow exists. If the PCM commands purge and sees that the switch is closed (indicating no detected purge flow) P0446 is set.
A code P0446 could mean one or more of the following has happened: Bad vacuum switch
Broken or damaged EVAP line or canister
Open in PCM purge command circuit
Open or short in Voltage feed circuit to Purge Solenoid
Faulty purge solenoid
Restriction in EVAP solenoid, line or canister
Corrosion or resistance in purge connector
What I recommend is first having the system fogged to determine if there is a leak in the system. Trying to find it without fog is very difficult. If no leaks are detected, then check for open circuit to the purge solenoid, bad purge solenoid, restriction in the line or the canister, or resistance in purge connector (common). If all is good, then the next step is the PCM.
I hope this helps. I realize it is confusing, so if you have other questions, let me know.