The VSV for CCV is open under normal conditions. When the VSV for EVAP is used to purge the evaporative emissions from the fuel tank into the intake manifold, air is drawn from the fuel tank into the charcoal canister. Also, the VSV for CCV has a function that relieves the pressure in the case that the pressure inside the fuel tank has rapidly increased. Also, it creates a vacuum inside the fuel tank in unison with the operation of the VSV for EVAP and leak tests are performed using this vacuum.
When the VSV for CCV remains closed (closed malfunction), the vacuum created inside the fuel tank cannot be relieved. When the VSV for CCV remains open (opened malfunction), it cannot create a large vacuum.