All P0442 tells us is that a small leak was detected in the Evaporative emissions system, which is the system that incorporates the carbon canister to store fuel tank vapors until they can be routed back to the intake manifold to be burned, rather than have them vent into the atmosphere. The evap emissions system has a self-check to determine if the system is sealing and working properly. The best the typical DIY'er can probably do is do a visual inspection of the evaporative emissions systems to make sure there are no disconnected, split or otherwise leaking hoses. More than that requires a scantool to command the vent control valve and to monitor the evap pressure sensor voltage. Also required is a Mighty-vac air/vacuum pump, evap test port adapter, a smoke machine (or a spray bottle of soapy water if a smoke machine is not available).