GM-GMC: 2000GMC 1500 Sierra, sierra engine, solenoid valve

Question
engine light on and engine code is P0442 HOW CAN I FIX IT

Answer
That particular code generally means there is a problem with the EVAP emissions system.  The most common problem is a gas cap being left loose or not secured properly causing a leak in the system.  The second most common problem would be a vent solenoid valve.  This is a small valve which is responsible for closing the vent to the fuel tank under certain conditions.  If you look between the cab and the box on the drivers side you can see a portion of it.  The only way to tell if that valve is functioning properly is to turn it on and off with a scanner and listen for a clicking noise.  If no noise, test for power and ground.  If it were my vehicle I would tighten the gas cap and disconnect the battery to reset the light and drive it to see if the light comes back on.
hope this helps