There's no single, readily accessible fuel shutoff switch on a 1999 Chevy Express van like you might find on some older vehicles. Fuel delivery is controlled electronically. To stop the fuel supply, you'll need to either disconnect the fuel pump relay or, in an emergency, disconnect the negative battery cable.
Important Note: Disconnecting the negative battery cable will disable *all* electrical systems. Only do this as a last resort in an emergency situation. Improperly disconnecting the battery can also damage certain electronic systems.
