Ford Workshop Service and Repair Manuals

General

In a communication network (data bus system), the various modules of different systems are connected to one another via one or several lines.

The sole purpose of the data bus system is the transmission of data between the connected modules themselves, as well as between the connected modules and the WDS (Worldwide Diagnostic System).

In a data bus system, complete data blocks are transmitted instead of single in/out pulses. In addition to the actual information, these data blocks also contain data regarding the address of the module to be addressed, the size of the data block and information for monitoring the content of each individual data block.

Data bus systems offer various advantages:

• Simplified data transmission between the modules due to a standardized protocol
• Fewer sensors and connectors
• Improved diagnostic options
• Lower costs

The diagnostic tester is connected to the various data bus systems and to the voltage supply via the standard 16-pin data link connector (DLC). The signal for the module programming is also transferred via the DLC.

If, in a data bus system, there is a break in one or both lines or a short to ground or a short to battery positive is present, then communications between the modules and the diagnostic tester will either be interrupted or no longer possible at all.

In order to be able to establish communications with one another, the modules of the individual systems must use the same language. This language is called a protocol.

At present, Ford uses three different data bus systems. Depending upon model and equipment level, all three data bus systems are used. Each of these data bus systems has its own protocol.

• SCP (Standard Corporate Protocol) bus. This consists of two twisted wires. It is used for communication between the modules themselves and between the modules and the diagnostic tester. Depending upon engine version and year of manufacture, a third wire (ACP bus) is used for programming the PCM. This bus is only used in conjunction with the SCP bus.
• ISO (International Organization for Standardization) 9141 bus. This consists of a single wire and is used exclusively for communication between the modules and the WDS. The fault memories of the various modules are read out via the ISO 9141 bus.
• CAN (Controller Area Network) bus. This consists of two twisted wires and operates serially (data is transmitted sequentially). It is used for communication between the modules themselves and between the modules and the WDS. The modules are connected to the data bus in parallel. New modules can be incorporated easily, without modifying the other wiring or modules. The transmitted data is received by every module connected to the CAN bus. As each data packet has an identifier, in which the priority of the message is determined as well as the content identification, each module can detect whether or not the data is relevant for its own information processing. This enables several modules to be addressed with a particular data packet and supplied with data simultaneously. For this purpose, it is ensured that important data (for example from the ABS) are transmitted first. The other modules are only able to submit their data to the data bus after the high-priority messages have been received.

In order to guarantee a high degree of error protection, two 120 Ohm terminating resistors are installed in the CAN bus. These are integrated in the first module connected to the CAN bus and in the last module connected to the CAN bus respectively and are used for suppression as well as the elimination of voltage peaks. In order to ensure correct functioning of the data bus system, the modules must always be connected with an integral terminating resistor.

The advantages of the CAN bus are:

• Minimization of wiring requirements.
• High degree of error protection (fault / fail-proof).
• Robustness.
• Good extendibility.
• Prioritization of messages.
• Inexpensive.
• Automatic repetition of faulty messages.
• Independent system monitoring and option for automatic disconnection of faulty modules from the data bus.

Network Components

In the Ka, all three data bus systems are used, depending upon year of manufacture and model version.

ISO 9141 bus

The ISO 9141 bus connects

• ABS module
• Restraint control module (RCM)
• Door lock module
• Generic electronic module (GEM)
• Powertrain control module (PCM)

to the diagnostic tester, via the DLC. The number of modules is dependent upon the vehicle equipment level as well as the year of manufacture. The module fault memories are read out via this data bus.

ISO 9141 bus overview

NOTE:The number of modules is dependent upon the vehicle equipment level and the year of manufacture.