A fuel shutoff solenoid is an electronic switch that automatically stops the fuel flow from the tank to the engine. The valve is normally in the open position; however, a loss of electrical power to the valve or activating a switch in the vehicle closes the valve to stop fuel flow. Manufacturers install such switches on both gasoline and diesel vehicles.
The fuel shutoff solenoid is located in the fuel pump, but the electronic switch is inside of the driver's compartment. Once the switch is activated, the flow of fuel stops, and the engine no longer operates. Many of these switches also have a manual override feature to shut off the fuel in the event of a power failure. The solenoids are useful in stopping fuel flow in the event of an accident.
With diesel technology, which has a longer history of fuel injection, the shutoff valve also serves as a kill switch to stop the engine from running. In older Mercedes vehicles, the switch operated from the vacuum system, and activating the vacuum switch stopped the fuel flow and the engine. Manufacturers replaced the vacuum switch with a more-reliable electronic solenoid version on newer vehicles, eliminating the frequent need to open the hood and manually activate the switch from the vacuum system.