Passive Anti-Theft System (PATS) Transceiver
WARNING: This page is about a different car, the 2017 Lincoln Navigator and 2017 Ford Expedition. 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 lock cylinder. When the ignition changes to RUN or START, the BCM activates the PATS transceiver. Once the transceiver is activated, it in turn activates the key in the ignition lock cylinder and receives the key data. Once the transceiver receives the key data, it sends the data to the BCM.