P0442 and P0455 are the ones generally associated with a leak in the vapor dome of the fuel system (like a leaky gas cap).
P0441 refers to improper purge flow.
An empty gas tank is not truly empty - it is filled with gasoline vapors. Filling it with liquid fuel at the pump will push all that vapor out of tank. The EPA and CARB don't want those vapors pushed out into the atmosphere, so your fuel tank is vented to atmosphere THRU a canister filled with charcoal. As the vapors pass through the bed of charcoal, they condense and collect on/in the coal.
There is a line that runs from the charcoal canister to the intake manifold, with a computer-actuated valve (called the purge valve) between them. From time to time, the computer will open the purge valve and allow the engine to suck on the charcoal canister, removing the fuel vapors and condensation.
The computer knows when it is ASKING for purge flow - but it is also mandated that it diagnose/determine if the action actually took place. Usually there is a pressure and/or flow sensor on the line that runs between charcoal canister and intake manifold. When the valve opens and the engine sucks on the canister - there should be either flow detected, or perhaps a slight pressure drop. A lack of flow and/or pressure indicates there is not actual purge flow --> and thus, a malfunction.
The valve itself has it's own circuit functionality diagnostics, which are basic OBD-1 codes. Because you're not getting any circuit fault trouble codes, I suspect your valve and sensor are operating correctly, but you have a disconnected, broken or leaking purge flow line.
Hope that helps.