Encoded Ignition Key
WARNING: This page is about a different car, the 2001 Ford Excursion and 2000 Ford Excursion. However, it is still accessible from the selected car via links, so may be relevant.
The encoded ignition key is much larger in size than a regular key to accommodate electronics located inside plastic cover. Each encoded ignition key must be programmed into Passive Anti-Theft System (PATS) control module. When ignition switch is in START or RUN position, the PATS control module initiates the encoded ignition key interrogation process.