Body Control Systems: Description and Operation

Communications Network

OVERVIEW

A number of different types of communication network are incorporated into the vehicle wiring harnesses for the transmission of commands and information between control modules. The configuration installed on a particular vehicle depends on the model and equipment level.

The communication networks available on the vehicle are:
^ Local Interconnect Network (LIN) bus
^ Medium speed Controller Area Network (CAN) bus
^ High speed CAN bus
^ Media Orientated System Transport (MOST) ring





LOCAL INTERCONNECT NETWORK BUS
The Local Interconnect Network (LIN) bus is a low speed broadcast network that employs master and slave components. The master component transmits a message along a single wire to the slave components identifying which slave is to respond. The message has a header (slave identifier) and an empty data field. The identified slave component fills the data field with the relevant information and returns a message to the master component along the same wire.

CONTROLLER AREA NETWORK BUS
The Controller Area Network (CAN) bus is a high speed broadcast network where control modules automatically transmit information every few microseconds. Information is broadcast down a pair of twisted wires, known as 'CAN high' and 'CAN low'. Information is transmitted on the CAN bus as a voltage difference between the 2 wires.

Two CAN bus networks are used on the vehicle; medium speed and high speed, with the Central Junction Box (CJB) acting as a gateway between the 2 networks. The table below shows the wire colors used on both networks.





MEDIA ORIENTATED SYSTEM TRANSPORT (MOST) RING
The Media Orientated System Transport (MOST) ring uses fiber optic cables to transport data and audio signals around the information and entertainment system. The fiber optic cables are arranged in a ring, with each unit on the ring having a 'MOST in' and 'MOST out' connection.

The MOST ring is a synchronous network. A timing master supplies the clock and all other components on the ring synchronize their operation to this clock. The timing master for the MOST ring is the integrated control module.

When handling MOST fiber optic cables the following precautions should be observed:
^ After disconnection of any cables carefully install appropriate dust caps to protect the mating faces of the connectors from damage and contamination.
^ Avoid introducing bends of less than 25 mm (0.98 inches) radius or kinks into the fiber optic cable during service or repair. Tight bends or kinks could impair operation, cause immediate system failure, or future system failure.
^ Avoid excessive force, strain or stress on the fibers or connectors especially permanent stress after reinstallation.

Ring Break Diagnostics
Incorporated into the Auxiliary Junction Box (AJB) is a Ring Break Diagnostics (RBD) link. The RBD link houses a copper link which when removed initiates the ring break diagnostics mode. The ring break diagnostics mode allows the technician to locate an optical fiber break in the MOST ring. To initiate the ring break diagnostics mode, carry out the following process:
^ Connect the Land Rover approved diagnostic system.
^ Ensure the vehicle is in power mode 4 or greater.
^ Remove the RBD link for the length of time specified by the Land Rover approved diagnostic system.
^ Replace the RBD link.

After approximately 30 seconds a Diagnostic Trouble Code (DTC) will be logged in the Integrated Control Module, identifying the location of the fault. The DTC can be read and interrogated using the Land Rover approved diagnostic system.

CONTROL DIAGRAM - LIN BUS (SHEET 1 OF 2)





CONTROL DIAGRAM - LIN BUS (SHEET 2 OF 2)





CONTROL DIAGRAM - MEDIUM SPEED CAN BUS





CONTROL DIAGRAM - HIGH SPEED CAN BUS





CONTROL DIAGRAM - MOST