Solenoid Tank Valves
WARNING: This page is about a different car, the 2002 Ford Pickup. However, it is still accessible from the selected car via links, so may be relevant.
The solenoid tank valve receives VPWR from Inertia Fuel Shutoff (IFS) switch. If IFS is tripped for any reason (i.e. accident), or if ignition switch is turned on and there is no tach speed signal received by PCM, solenoid tank valves will be closed.
If ALT fuel system automatically switches to GAS mode, solenoid tank valves will close. This is triggered when Fuel Rail Pressure Sensor (FRPREAB) PID drops to 68.8 psi (4.84 kg/cm2 ) on CNG, or 24.6 psi (1.73 kg/cm2 ) on LPG.