Abstract: A locking fuel cap arrangement for preventing unauthorized access to the fuel tank of a vehicle. The filler cap is provided with a plurality of ratchet teeth formed on the underside thereof. A spring-biased electrical solenoid operates a pawl that is adapted to engage the ratchet teeth and prevent removal of the filler cap and to disengage the ratchet teeth when the solenoid is energized. A lock-out pin automatically assumes an interference position when the solenoid is energized to prevent re-engagement of the pawl and ratchet teeth after the solenoid is de-energized, thereby permitting removal of the filler cap. Upon subsequent re-installation of the filler cap after removal, the lock-out pin is automatically rotated into a non-interfering position by the clockwise rotation of the filler cap as it is threaded onto the filler neck, thus permitting the pawl to re-engage the ratchet teeth in the filler cap.