A Controller Area Network (CAN Bus) is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other in applications without a host computer. It is a message-based protocol, designed originally for multiplex electrical wiring within automobiles, but is also used in many other contexts.

Bascailly everything in the car talks with each other. It's not like older cars were they have a PCM and BCM that work by themselves and nothing really talks with eachother besides maybe a security system to prevent someone from drivign away with the car.