Information Bus: Description and Operation

Description

General

A number of different types of data bus are incorporated into the vehicle wiring harnesses for the transmission of commands and information between ECU's. The bus configuration installed on a particular vehicle depends on the model and equipment level:
- Controller Area Network (CAN) bus. A network connected between the brake, powertrain, steering and suspension related ECU's
- Diagnostic buses. Two networks that directly and indirectly connect the diagnostic socket to all of the of the ECU's installed on the vehicle
- I bus. A network connected between ECU's of the Information' systems
- K bus. A network connected between ECU's of the 'body' systems
- M bus. A network connected between the HEVAC ECU and motors on the heater assembly
- P bus. A network connected between the BCU and Peripheral ECU's

Serial interface circuits in the ECU's transmit and receive commands and information on the buses as digital messages. ECU's connected to the same bus use a common protocol (format) and baud rate (transmission speed) for the messages they transmit. The protocol and baud rate varies between bus networks. To enable messages to be exchanged between ECU's from different bus networks the instrument pack provides a communication gateway. A microprocessor in the instrument pack converts and/or re-transmits messages between bus networks.

The CAN bus is a high speed broadcast network where the ECU's automatically transmit information on the bus every few microseconds. The other buses are low speed networks which are mainly event driven i.e. an ECU outputs a message only in response to a request message from another ECU or a hard wired input from a switch or sensor.

A twisted pair of wires are used for the CAN bus and single wires are used for all of the other buses. Bus wires can be repaired using crimped connections. The unwound length of CAN bus wires must not exceed 40 mm (1.6 in).

Data Bus Types







The diagnostic socket is connected to all of the ECU's on the bus networks either directly, via the diagnostic buses, or indirectly via the instrument pack. The diagnostic socket is located in a pocket in the fascia, next to the driver's side A post.

Diagnostic Socket