Fuel vapors are stored in the charcoal canister, then burned later when the engine is running. The Engine Computer turns on the solenoid to allow those vapors to enter the engine, then it expects to see a change in the exhaust gas. It also expects to see a pressure change in the vapor system when that solenoid opens the valve. The computer detected a problem and set the code, but you don't know if there was proper flow that wasn't measured, if there was no flow due to blockage in the hose or valve, or if the valve is defective and not opening. The code only tells you why the computer is not happy, it doesn't tell you the cause of that unhappiness. That is where the troubleshooting begins. Mechanics have entire books on the steps needed to isolate the problem. Usually it's not a big problem but it's best left to an experienced mechanic. What you can do yourself first is to check for any small hoses that are disconnected, pinched, or have loose clamps.