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

MODEL 215 with Engine 113.991

MODEL 220 with Engine 113.991

MODEL 230 with ENGINES 113.992 /995

Fig 1: Identifying CAN Data Bus Function Diagram

Courtesy of MERCEDES-BENZ USA

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) engine CAN data bus (CAN-C) for the powerplant and chassis systems and the slower (83.3 kbit/s) body CAN data bus (CAN-B) structure for the vehicle interior.

In addition for the vehicle diagnosis with STAR DIAGNOSIS there is a diagnosis CAN data bus (CAN-D) 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, electronic ignition switch control unit and the steering column module are connected with both the body CAN data bus and the engine 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 is possible via a STAR DIAGNOSIS menu.

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

ME-SFI control unit, location/task/design/function

GF07.61-P-5000AM