1997 Ford Expedition Owner's Manual - Page 66

Controls and features ANTI-THEFT SYSTEM Passive anti-theft system Your ignition key has a unique imbedded transponder which engages engine electronics and allows the vehicle to be started. Without the use of your special ignition key, the vehicle will not start. During each vehicle start, the coded key is read by the anti-theft system. If the key's ID code matches the code in the anti-theft system, the vehicle is enabled to start. Your vehicle is equipped with two electronically coded keys. Additional spare keys can be purchased through your dealer or selected retailers. Be sure to purchase coded keys with the Ford logo to ensure proper functionality. If both supplied keys are lost or stolen, the vehicle and any other keys must be reinitialized by the dealer. A theft indicator in the instrument cluster provides operating status of the anti-theft system. For more information on this indicator and its function, refer to Warning and indicator lights in the Instrumentation chapter. THEFT Programming spare keys Use one of the two electronically coded keys supplied with your vehicle to program additional keys: 67