Ignition Switch System: Start
WARNING: This page is about a different car, the 2020 Ford F-150. However, it is still accessible from the selected car via links, so may be relevant.
When the ignition switch is placed in the START position, the switch routes voltage through the ON-designated and START-designated circuits to the BCM.
The BCM interprets this as the ignition start mode and communicates the ignition mode to the other modules by sending an ignition status message over the CAN. Additionally, the ignition switch routes voltage to the PCM indicating a request to start the vehicle.
The START-designated circuit is only used for vehicle starting.