Controller Area Network (CAN Bus)
A high-speed multiplex communications network that allows multiple vehicle modules to communicate with each other.
The Controller Area Network (CAN bus) is a specialized communication network that allows the vehicle's onboard computers—such as the engine control module, transmission controller, ABS module, and body control module—to share data with each other without complex dedicated wiring. It uses a twisted pair of copper wires (CAN High and CAN Low) to transmit digital messages between modules at high speeds.
Instead of running separate wires for every sensor to every computer, a sensor reading (like vehicle speed) is broadcast onto the CAN bus by the ABS module, and any other module that needs that data (like the instrument cluster or ECU) reads it off the network. This multiplexing reduces vehicle weight, simplifies wiring harness design, and improves system response times.
If a fault occurs on the CAN bus, such as a shorted wire, a bad connector pin, or a failing module that 'spams' the network, communication will break down. This causes multiple warning lights to illuminate, key systems to stop working (like the speedometer dropping to zero), and will store 'U-series' network codes. Diagnostic involves measuring network resistance (nominally 60 ohms) and using an oscilloscope to analyze data packet signals.