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 vehicle operator controls all speed control system features through the speed control switch pod on the face of the right horizontal spoke of the steering wheel. When a push button of the switch pod is depressed, it provides a hard wired resistor multiplexed analog input to the Body Control Module (BCM). The BCM is a gateway to the Controller Area Network (CAN) data bus and not only reads the hard wired speed control switch and stop (brake) lamp switch inputs, but also relays these inputs to the Powertrain Control Module (PCM) over the CAN bus.