The VSV for CCV is open under normal operating conditions. When the VSV for EVAP is used to purge the evaporative emissions from the fuel tank into the intake manifold, fumes are drawn from the fuel tank into the charcoal canister. The VSV for CCV has an additional function that relieves the pressure when the pressure inside the fuel tank has rapidly increased. Finally, the VSV for CCV is used in unison with the VSV for EVAP to create a vacuum inside the fuel tank and leak tests are performed using this vacuum.
The ECM checks for a VSV for CCV "stuck closed" malfunction by commanding both valves (VSV for EVAP and VSV for CCV) open at a time when the fuel tank is at atmospheric pressure. If the fuel tank develops high negative pressure (vacuum) and it remains in that state for more than 4 seconds, the ECM determines that the VSV for CCV (vent) is stuck CLOSED. The ECM will turn on the MIL and a DTC is set. This malfunction is detected regardless of the engine coolant temperature.
The ECM checks for a VSV for CCV "stuck open" malfunction by commanding both valves closed at a time when the fuel tank should have developed a high negative pressure (vacuum). If the fuel tank did not develop the proper high negative pressure (vacuum), the ECM concludes that the VSV for CCV must have been "stuck open". The ECM will turn on the MIL and a DTC is set.