CAN data bus, function - GF54.00-P-0005KE
Model 203 with ENGINE 271.942
Model 209 with ENGINE 271.942
Except model 203 as from 04/2004 up to 11/2004
For model 203 as from 04/2004 up to 11/2004
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 E lectro M agnetic C ompatibility (EMC [EMV])
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 data bus 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 data bus).
The sum of the data blocks, the short break between two transmission intervals and additional 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 a fast (500 kbit/s) engine CAN data bus (CAN C) for the drive and chassis systems and a slower (83.3 kbit/s) body CAN data bus (CAN-B) structure for the vehicle interior.
In addition to this external vehicle diagnosis using STAR DIAGNOSIS has a diagnosis CAN data bus (CAN-D) with a speed of 500 kbit/s.
A separate (local) CAN data bus link is set up between the control unit NOX and the ME control unit.
The interface of the three CAN data buses (gateway) is located in the EIS [EZS] control unit (except for model 203 as from 04/2004 up to 11/2004). In model 203 as from 04/2004 up to 11/2004 the interface of the three CAN data buses (gateway) is located in the central gateway control unit.
The instrument cluster, steering column module and EIS [EZS] control unit (for model 203 as from 04/2004 up to 11/2004) are connected both to the body CAN data bus and the engine CAN data bus and exchange data with both data bus systems. But they do not act as an interface (Gateway) between both data bus systems!
When a control unit is changed the new control unit has to 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 I nterfaces for E lectronics in motor vehicles) is used for all control units of the CAN data bus.
| ME-SFI control unit, location/task/design/function | N3/10 | GF07.61-P-5000KE |