CAN data bus, function - GF54.00-P-0005GZ

MODEL 164 with ENGINE 156.980

MODEL 251 with ENGINE 156.980

Fig 1: CAN Data Bus Function Diagram - Engine 156.980

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

CAN stands for "C ontroller A rea N etwork". This is an electrical bus system for carrying data over two wires.

The tasks are:

Data transfer between individual control units
Readying sensor signals for several systems
Reducing the number of electric cables
Improving the electromagnetic compatibility (EMC)

The CAN data bus consists of a special twisted two-core data line that connects all CAN users (control units) in parallel.

The two lines of the data line must not be mixed up (low level/high level). The ME control unit always represents a terminal with regard to bus adaptation.

A 120 Ω terminating resistor is therefore installed in the motor electronics control unit.

The data are transmitted digitally over the CAN databus at various intervals. The individual data blocks are defined in a data protocol and it is specified which data are received or transmitted by a control unit. Each connected control unit is able to transmit or receive data (bidirectional bus).

The sum of the data blocks, the short break between the two transfer intervals and other properties of the CAN data bus are checked constantly. Detected faults are stored and placed in the fault memory.

In the vehicle a distinction is made between the fast (500 kbit/s) drive train CAN data bus for the engine systems, transmission systems and chassis systems and the slower (83.3 kbit/s) interior CAN data bus for the systems in the vehicle interior.

In addition for vehicle diagnosis there is a diagnosis CAN data bus with a speed of 500 kbit/s.

The interface between the three CAN data buses (Gateway) is located in the central gateway control unit.

The instrument cluster, the EIS [EZS] control unit and the steering column module are connected both to the interior CAN data bus and to the drive train CAN data bus and exchange data with both data bus systems. However they do not serve as an interface (Gateway) between tow data bus system

When a control unit is replaced, the new control unit must be coded again.

This control unit coding takes place via a STAR DIAGNOSIS menu.

The international standardized network management "OSEK" (O pen systems and their I nterfaces for E lectronics in motor vehicles) is used for all control units of the CAN data bus.

ME-SFI [ME] control unit, component description

GF07.61-P-6000AMG