DTC P1491: Vacuum Cut Valve By-Pass Valve: Description
WARNING: This page is about a different car, the 2002 Nissan Sentra. However, it is still accessible from the selected car via links, so may be relevant.
The vacuum cut valve and vacuum cut valve by-pass valve are installed in parallel on the EVAP purge line between the fuel tank and the EVAP canister. See Fig 1 . The vacuum cut valve prevents the intake manifold vacuum from being applied to the fuel tank. The vacuum cut valve by-pass valve is a solenoid type valve and generally remains closed. It opens only for on board diagnosis. The vacuum cut valve by-pass valve responds to signals from the ECM. When the ECM sends an ON (ground) signal, the valve is opened. The vacuum cut valve is then by-passed to apply intake manifold vacuum to the fuel tank.