CAN data bus, function - GF54.00-P-0005T
MODEL 211, 219 with ENGINE 113.990
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 interchange between the individual control units
- Readying sensor signals for several systems
- Reducing the number of wires
- 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 wires of the data line must not be mixed up (low level / high level). The motor electronics (N3/10) control unit is always a consumer 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 systems and chassis systems and the slower (83.3 kbit/s) body CAN data bus (CAN-B) structure for the vehicle interior.
In addition for external vehicle diagnosis using STAR DIAGNOSIS there is a CAN diagnosis data bus (CAN-D) with a speed of 500 kbits/s.
The interface between the three CAN data buses (Gateway) is located in the central gateway control unit (N93).
The instrument cluster (A1), electronic ignition switch control unit (N73) and steering column module (N80) are connected both with the CAN data bus, body and with the CAN data bus, engine and exchange data with both data bus systems. However, they do not serve as an interface (gateway) between both data bus systems!
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" (open systems and their interfaces for electronics in vehicles) is used for all control units on the CAN data bus.
| ME-SFI control unit, location/task/design/function | GF07.61-P-5000AM |