Encoded Ignition Key
WARNING: This page is about a different car, the 1997 Ford Expedition. However, it is still accessible from the selected car via links, so may be relevant.
When ignition is in start or run, PATS module initiates the encoded ignition key interrogation process. PATS module supplies both power and carrier signal to transceiver module to momentarily energize ignition key. After energize period has expired, key transmits its identification code to transceiver module. This encoded ignition key is much larger in size to accommodate the electronics located inside plastic cover.