Passive Anti-Theft System (PATS) Transceiver
WARNING: This page is about a different car, the 2013 Ford Explorer. However, it is still accessible from the selected car via links, so may be relevant.
The PATS transceiver reads any key that is placed in the ignition. When the ignition is turned to the ON or START position, the BCM activates the PATS transceiver. Once the transceiver is activated, it in turn activates the key in the ignition and receives the key data. Once the transceiver receives the key data, it sends the data to the BCM .