Ford Workshop Service and Repair Manuals

Network components

Dependent on the vehicle accessories version, two data bus systems are used:

• Controller Area Network (CAN) bus
• Local Interconnect Network (LIN) bus

Due to the increased number of modules and the resulting continued increase in data transfer, three different CAN bus systems are used. Essentially, they only differ in terms of their data transmission rates and application areas. In order to be able to distinguish between the individual CAN bus systems, the CAN bus system with the higher data transfer rate is referred to as the high-speed (HS) CAN bus, the CAN bus system(s) with the lower data transfer rate as the mid-speed (MS) CAN bus or multimedia (MM) CAN bus. The latter operate at a slower speed and are used primarily for communications in the areas of comfort electronics and multimedia systems. Two interfaces (gateways) are used in order to exchange data between the HS CAN bus, MS CAN bus and the MM CAN bus. The provide the connection between the three CAN databus systems and are installed in the GEM and in the electronic instrument cluster.

The number of modules which are connected to the three databus systems depends on the equipment level of the vehicle.

Controller area network (CAN)

General

In the past, a separate cable was needed for every command and every message. The use of networks has enabled an increase in functionality without additional cables.

The demand for greater functionality in vehicles, both due to legal requirements and in order to meet customer demands, results in increasing complexity of vehicle systems.

The Controller Area Network (CAN) was developed as part of the effort to achieve greater flexibility of the electrical systems. It allows a large number of different control commands and messages to be sent and received on the same cable system.

The number of control commands and messages which can be processed by a network depends on factors like the data transfer rate and the length of the messages. The SMAX/Galaxy network, which is based on a Controller Area Network (CAN), is capable of transferring over 500 different signals and approx. 100 messages. These messages are also described as transmission blocks and may contain several signals.

Advantages of a network

Easy integration of additional functions and accessories

As the control modules in the network are already connected to each other and can easily accept further information, only the following steps are necessary:

• Connection of the sensors to the nearest control module
• Connection of the component which is to be actuated to the nearest control module
• Software-based adaptation of the module configuration

This means that the overall length of cabling and the number of components in a vehicle are reduced compared to before.

One example of this is the integration of the speed control system.

Before the introduction of the network, control modules, switches, vacuum pumps, vacuum servos, hoses and wiring harnesses were needed for this system.

Following introduction of the network, only one switch and the software for adaptation of the vehicle configuration are required.

Easier to introduce logical functions

The term "logical functions" is used to describe the concept whereby certain events trigger certain responses. For example, the system is programmed in such a way that if a tail lamp fails a message is sent via the Controller Area Network (CAN) to the electronic instrument cluster to warn the driver.

A logical function can be introduced by merely reprogramming the affected control modules. In the above case this would be the generic electronic module (GEM) and the electronic instrument cluster. The number of components and cables remains the same.

Simple adaptation of systems to customer demands and market requirements

Vehicle functions can be adapted to customer demands and market requirements, e.g. in the case of the rear fog lamps. In some countries two rear fog lamps are used, whereas in other countries only one fog lamp is used on the driver's side. In the past it was necessary to stock different spare parts for different markets. Now a single part is sufficient to cover all markets - it just needs to be programmed for the specific market.

Use of similar basic systems for entire series

Similar networks (hardware) can be used for a wide variety of different vehicles.

The vehicles only differ in terms of:

• The individual components (modules, sensors, actuated components etc.) which are connected to the system.
• The task(s) of the components.
• The definition of the components as standard/optional/accessories.
• The configuration/programming of the system.

The layout of the network.

General

The network is made up of a range of control modules (these are also referred to as nodes) which are connected to each other via two communication cables. Each module has its own voltage supply and ground connection and receives messages and control commands via both communication cables.

In the event of a break in the circuit, the modules beyond the break cannot communicate with other parts of the network.

Network areas with high and low data transfer rates

The network consists of two parts. The area with the higher data transfer rate (HS CAN bus) transmits signals and messages between the generic electronic module (GEM) and control modules which are mostly located in the engine compartment. The area with the lower data transfer rate (MS/MM CAN bus) transmits signals and messages between the generic electronic module (GEM) and the control modules in the passenger compartment and in the luggage compartment.

The generic electronic module (GEM) represents the interface between the two areas and converts the data transfer rate up or down to allow the two areas of the network to communicate with each other.

Data transfer rates

The Controller Area Network (CAN) uses two data transfer rates.

• The HS CAN bus (high data transfer rate) transfers data at a rate of 500 kBit/s.
• The MS/MM CAN bus (low data transfer rate) transfers data at a rate of 125 kBit/s. 1 kBit/s = 1024 Bit per second (1 Byte = 8 Bit).

Terminating resistor

In order to avoid reflections and interferences in the CAN bus network, a terminating resistor is provided for bridging purposes at both ends of the CAN. Each terminating resistor has a resistance value of 120 Ohm.

• For the HS CAN bus, the terminating resistors are located in the generic electronic module (GEM) and in the powertrain control module (PCM).
• For the MS/MM CAN bus, the terminating resistors are located in the generic electronic module (GEM) and in the electronic instrument cluster.

The two resistors are connected in parallel. The resistance values are as follows:

• When the CAN bus is intact, the resistance is approx. 60 Ohm in both areas of the network.
• In the event of a short circuit between the communication lines the resistance is approx. 0 Ohm.

Controller Area Network (CAN) Standard

General

The CAN bus is a standardized system for multiplex communication. This means that multiple control modules can use the same wires for communication without causing interference between the different signals.

The Controller Area Network (CAN) Standard specifies the following:

• The use of two wires (CAN H and CAN L)
• The voltage amplitudes
• The structure of the messages
• The way in which transmission faults are handled

The lines CAN H and CAN L

The lines CAN H and CAN L must not be confused with the different data transfer rates HS CAN bus and HS CAN bus. The lines CAN H and CAN L are the paths on which signals are transmitted within the multiplex communication system.

Communications take place at different voltages via two separate wires which are twisted in pairs. As a result, the network is less susceptible to interference.

The same message is put out at the same time on both wires with different voltages.

• Binary signal 0 = 2.5V on CAN H and on CAN L
• Binary signal 1 = 4V on CAN H and 1V on CAN L

The average potential difference between CAN L and ground is approx. 2.3V, or approx. 2.8V between CAN H and ground.

These measured values refer to "normal" communications in the Controller Area Network (CAN), i.e. cases in which no faults have occurred which would cause the modules to send out error messages.

NOTE:Certain modules, such as the restraints control module (the module for the SRS system) and the ABS module or ESP module communicate with their relevant sensors via a so-called internal CAN bus. The internal CAN bus systems have nothing to do with the communications on the general CAN bus. Instead, they are only used for the purpose of transmitting data between sensors and associated modules.

Messages in the Controller Area Network (CAN)

A message comprises the following parts:

• An identifier which indicates the identity and priority of the message
• Information data (value, information etc.)
• A check sum which is used to check whether the message is received in full
• And end signal which signals the end of the message

A complete CAN message is referred to as a signal frame.

Priority

Conflicts may arise in a network if several control modules try to send messages at the same time as each other. This could for example be the case if the driver applied the brakes while the front passenger adjusted the A/C settings and a rear passenger operated the electric rear window regulators. The messages need to be prioritized so that safe operation can be ensured. In addition, any delays arising as a result of the prioritization process must be kept within limits so that the customer preferably does not notice them at all.

In order to avoid conflicts and delays and to ensure perfect operation of the systems, a fixed ranking order applies to the messages.

The priority of a message is defined by the number of zeros at the start of the message; the more zeros, the higher the priority.

Prioritization takes place as follows:

• If the network is available, all modules waiting to send a message deliver the first bit of their message.
• All modules register the signals sent out on the network.
• If a zero is sent out by a module then the modules which sent out a "1" wait until the network is available again.
• The modules with a zero then send the second bit of their message.
• If a zero is sent out by a module as its second bit then the modules with a "1" wait until the network is available again. This process is repeated.

The message with the highest priority, i.e. the message with the largest number of zeros at the start, is sent first.

The end of a message is made up of seven zeros. It shows the modules that the network is free again and that messages can be sent out again according to their priority.

Two message types

Two types of message are sent in the system:

• Periodic signal frames are sent regularly to indicate the current status of a parameter. They are used for types of information which change frequently, e.g. vehicle speed signals.
• Event-related signal frames are only sent if certain conditions are met. They are used for types of information which occur more rarely, e.g. the opening or closing of a window.

The messages may also incorporate an update bit which shows how "new" the message is.

The system always assumes that the messages reach the intended recipient, so no receipt acknowledgement signals are sent out. Replies are only sent in response to direct queries from other modules.

However, a receiver module also knows how often it should receive a particular status message. If the message is not received then the receiver module can launch an emergency running program and/or set a trouble code (DTC).

Compatibility

The modules must all speak the same language and be compatible with each other. As a result, a standardized communication protocol is used.

The language of the modules is contained in the signal configuration. If the signal configuration of a module does not match the configuration of the other modules than the module cannot communicate with them. This means that all modules must have a compatible signal configuration.

In order to check this, the generic electronic module (GEM) sends out an identification number for its signal configuration via the Controller Area Network (CAN). The other modules compare this number to their own number. If the identification does not match then the module stores a trouble code (DTC). The signal configuration is changed occasionally, so that new messages are added and old ones are removed.

Configurations

The following information is downloaded when a system is configured:

• Type of control modules contained (e.g. generic electronic module (GEM)) - task assignments for the individual modules (e.g. this is the module for the driver's door))
• Functions contained (e.g. alarm function on or off)
• Connected components (e.g. whether or not the inclination sensor is relevant for the alarm function)
• Output an input messages for each module
• Storage locations for various data

The configuration needs to be adapted for any accessories which are installed and needs to be downloaded again if a module is replaced. The diagnostic unit is used for adaptation and downloading.

NOTE:Two vehicles which otherwise appear identical may behave differently if they have different configurations. Parameters may have been changed by the customer or by the workshop.

Error management in the Controller Area Network (CAN)

General

The Controller Area Network (CAN) is monitored by the generic electronic module (GEM). If the GEM detects a fault in the CAN bus then a trouble code (DTC) is stored in the GEM. There are different types of DTC according to the fault type:

• No communications from the module
• Faulty communications

No communications from the module

The generic electronic module (GEM) knows which modules are in the Controller Area Network (CAN) and checks whether all modules are communicating. If a module is not communicating a trouble code (DTC) is set in the GEM. There is a trouble code (DTC) for every module.

Faulty communications

If the Controller Area Network (CAN) is in operation then the generic electronic module (GEM) continuously monitors the flow of information in the network. If the GEM determines that, for some reason, the communications in the CAN bus are interrupted, it can set a trouble code (DTC). The GEM has trouble codes for all parts of the CAN bus (one each for the HS CAN bus and the MS/MM CAN bus).

With the exception of the GEM, which only knows one type of DTC, each module uses two types of DTC in relation to communication faults. These are:

• Faulty messages
• Faulty configuration

As the GEM is the main module in the network, it does not have a DTC for faulty configuration.

Faulty messages

The control modules continuously monitor the flow of information in the Controller Area Network (CAN). If a module receives a message it cannot interpret it sends a fault message via the CAN bus. The modules also have function which allows them to detect any faulty messages they generate themselves. This prevents interference on the CAN bus. If there is a lot of interference in the network then any modules which cannot communicate properly can switch themselves off. This status is referred to as "databus OFF" - the module can no longer send or receive information.

To prevent the vehicle from coming to a sudden standstill or suffering a total loss of particular functions if a fault occurs in the CAN bus, certain modules have an emergency running mode. This means that modules which are required for driving or for safety aspects (e.g. the powertrain control module (PCM) or the transmission control module (TCM)) can maintain a restricted functionality on the basis of predefined or estimated data. For example, if communications to the transmission control module (TCM) are interrupted then the transmission will use a preselected gear which will enable the customer to at least drive to the nearest workshop. A module remains in "databus OFF" mode until the power supply to the module is switched off. If the power supply is reconnected the module attempts to re-establish communications.

Faulty configuration

The generic electronic module (GEM) transmits its configuration ID within the messages it sends out to other modules. To enable the modules in the Controller Area Network (CAN) to communicate with each other they must have the same configuration ID, as modules only look at messages carrying their own configuration ID. If the signal configuration of a module does not match the signal configuration of the GEM then a trouble code (DTC) is stored in the module with the faulty configuration.

NOTE:A module will save a trouble code (DTC) if it does not receive any messages from the generic electronic module (GEM). This also applies if there are any software errors in the module. If the circuit in the Controller Area Network (CAN) is interrupted then certain modules will also not receive any messages from the GEM.

Local Interconnect Network (LIN)

The Local Interconnect Network (LIN) bus is a standard which has been developed for cost-effective communications between intelligent sensors and actuators in motor vehicles. LIN is used wherever the bandwidth and versatility of CAN is not required.

The LIN specification comprises the LIN protocol, a standard format for describing a complete LIN network and the interface between a LIN network and the application.

A LIN network is made up of a LIN master and one or more LIN slaves.

The LIN network utilizes the master/slave principle for the purpose of bus access control. This has the significant advantage that few resources (CPU performance, ROM, RAM) are required for bus management in the slave module. The master is implemented in a control module or a gateway which has the necessary resources. All communication is initiated by the master. Consequently, a message always consists of a header, which is generated by the master, and a response from the slave.

The data transfer rate is in the region of up to 20 Kbit/s.

The LIN master knows the time sequence of all data which are to be transmitted. These data are transmitted by the corresponding LIN slaves (e.g. ultrasonic sensors) when requested to do so by the LIN master.

LIN is a single-wire bus, i.e. the data are transmitted across a single-stranded cable. Usually the same cable is also used to provide the supply voltage. The ground connection of the supply voltage also acts as the ground connection of the data transmission. No terminating resistors are used in the LIN network.