Theory Of Operation
WARNING: This page is about a different car, the 2015 Fiat 500. However, it is still accessible from the selected car via links, so may be relevant.
The Body Control Module (BCM) monitors the condition of the RKE (Remote Keyless Entry) Fob transponder. When a report comes back to the BCM that the transponder has an internal failure, the BCM will set the code.