Module Communications Network: Other Land Rover Discovery IV

GENERAL

Communication Network (Media Oriented System Transport MOST) Sheet 1 of 3

Note. P = MOST

Scheme 109

Communication Network (CAN bus) Sheet 2 of 3

Note. D = High speed CAN Bus; N = Medium speed CAN Bus

Scheme 110

Communication Network (CAN bus) Sheet 3 of 3

Note. D = High speed CAN Bus; N = Medium speed CAN Bus; O = LIN Bus

Scheme 111

A number of different types of data bus are incorporated into the vehicle wiring harnesses for the transmission of commands and information between modules. The bus configuration installed on a particular vehicle depends on the model and equipment level.

The available types of bus systems on the vehicle are

1. High speed Controller Area Network (CAN) bus
2. Medium speed CAN bus
3. Media Orientated System Transport (MOST) bus
4. Gigabit Video Interface (GVIF)
5. Local Interconnect Network (LIN) bus
6. Security Local Interconnect (SLIN) bus

Controller Area Network (CAN)

The CAN bus is a high speed broadcast network where the modules automatically transmit information on the bus every few microseconds. The other buses are low speed networks which are mainly event driven, i.e. an electronic control module outputs a message only in response to a request message from another module or a hard wired input from a switch or sensor.

A twisted pair of wires are used for the CAN bus and single wires are used for all of the other buses. Bus wires can be repaired using crimped connections. The unwound length of CAN bus wires must not exceed 40 mm (1.6 in).

Two CAN busses are employed on the vehicle

1. Medium speed
2. High speed

The medium speed bus connects the following control modules

1. Integrated Head Unit (IHU) or low line head unit
2. Heating and ventilation control module
3. Fuel burning heater
4. Park distance control
5. Tyre pressure monitoring control module
6. Central junction box

The high speed bus connects the following control modules

1. Steering angle sensor
2. Air suspension
3. Electric park brake
4. Electronic rear differential control module
5. Terrain Response™
6. Restraint control module
7. Engine control module
8. Transmission control module
9. Adaptive front lighting system control module
10. Antilock Braking System (ABS) control module

Both the medium and high speed CAN bus are connected to the Instrument cluster and the diagnostic socket at one end. The Medium speed bus terminates at the Central Junction Box (CJB), while the high speed bus terminates at the ABS control module.

Control modules are connected in either a loop, CAN in/CAN out, or a spur configuration. Should a control module that is looped fail that bus system will fail at that point. Should a spurred control module fail the rest of the bus system will be unaffected by the faulty control module.

Media Orientated System Transport (MOST)

The MOST bus uses a fibre optic cable to transport data and audio around the entertainment and information system. The fibre optic cable is arranged in a ring, with each unit on the bus having a MOST in and MOST out.

MOST is a synchronous network. A timing master supplies the clock and all other devices synchronize their operation to this clock. The timing master for the MOST network is the integrated head unit (IHU).

Key features of the MOST network are

1. Simple connectors
2. Reduced cabling
3. Support of asynchronous and synchronous data transfer
4. Support for up to 64 devices
5. High data transfer rate

When handling the MOST fibre optic cables the following safety precautions should be observed

1. The cable has a minimum bend radius of 25mm.
2. It is advisable not to look directly into the connector of a live cable.
3. The MOST cable cannot be repaired, replacement overlay harnesses will be available to replace damaged cables.

Gigabit Video Interface (GVIF)

The GVIF bus is a Sony proprietary bus for the transmission of video between a transmitter device and a display device. In this instance it is used to transmit video from the navigation computer to the Touch Screen Display (TSD) only.

Local Interconnect Network (LIN) bus

There are two LIN buses on the vehicle. One connects the Rain sensor, Sunroof and Memory seats to the central junction box and the other connects the BBUS to the central junction box.

The LIN bus has a master/slave configuration. Within the master is stored a 'schedule table' which is a list of all the LIN frames or packets in order of which one gets sent when and how many times within a particular cycle. The Master sends out a header on the bus which will identify to the slaves whose turn it is to transmit a frame. The slave then fills the space after the header with the contents of the frame. The frame identifiers are all sourced from the LIN specification, and the frame identifiers are grouped by the size of the frame in bytes. All the LIN nodes are optional fit, consequently there is a different schedule table for each permutation and the Bus master switches between these based on the information held within the car configuration file. The CJB also acts as a bi-directional gateway between the medium speed CAN bus and the LIN bus by passing signals between the two buses.

The bus is a single wire and operates at 9.6Kbit/s. The protocol used on the LIN bus is defined by the LIN consortium.

CAN Network Integrity Checks

In the event that one or more control modules are not communicating on either the Medium Speed (MS) or High Speed (HS) CAN Buses, checks can be performed to confirm the integrity of the CAN harness.

The following information is applicable to HS and MS CAN Buses accessible via the J1962 diagnostic connector.

Module Connections to the CAN Harness

Modules are connected to the CAN harness either in a 'loop' or 'spur' configuration. In the 'loop' type configuration the CAN harness loops into the module (via two connector pins) and then loops out of the module (via another two connector pins). In the 'spur' type configuration, a harness spur is spliced into the main 'backbone' of the CAN harness and the module is connected to the harness spur via two connector pins.

CAN Harness Architecture

For a detailed description of the CAN Networks and architecture, refer to the relevant Description And Operation section in the service information. REFER to

Communications Network

IDS Vehicle Integrity Test

If a control module is suspected of non-communication, the Network Integrity test application available on the manufacturer approved diagnostic system can be used to confirm if communication is possible between the control modules on the vehicle and the manufacturer approved diagnostic system (via the J1962 diagnostic connector). The results from the test can be used to determine if either a single module or multiple modules are failing to communicate.

CAN Terminating Modules

If the Network Integrity test indicates that one or more module on one of the CAN networks (HS or MS) are failing to communicate, there are several checks that can be made. The first step is to identify if both of the CAN terminating modules on each individual CAN Bus are communicating. If both CAN terminating modules for each individual CAN Bus are communicating (identified via the Network Integrity test), then it can be confirmed that the main 'backbone' of the CAN harness is complete. The main 'backbone' of the CAN harness consists of all the modules connected to the CAN harness via a 'loop' configuration and also includes the two terminating modules.

Communication with both CAN terminating modules via the Network Integrity test confirms the physical integrity of the main 'backbone' of the CAN harness (and the harness spur to the J1962 diagnostic connector). This means that there is no requirement to check the resistance of the CAN Network. This is because the standard check for 60 ohms across the CAN High and CAN Low lines will not provide any additional information regarding the physical condition of the CAN harness, beyond what has already been determined from the Network Integrity test.

Non-Communication of a Terminating Module

If a Network Integrity test reveals a terminating module is failing to communicate it can indicate a break in the main 'backbone' of the CAN harness. The first checks should always be to confirm the power and ground supplies to the non-communicating module are correct. Providing these are correct, the resistance between the CAN High and CAN Low lines at the J1962 connector can be checked to determine the integrity of the main 'backbone' of the CAN harness. After disconnecting the battery a reading of 120 ohms would indicate an open circuit in the main 'backbone' of the CAN harness. Alternatively, a reading of 60 ohms would indicate that there is no open circuit fault with the main 'backbone' of the CAN harness.

It is worth noting that even if one of the terminating modules is disconnected from the CAN harness, communications between the modules still connected may still be possible. Therefore communication between the manufacturer approved diagnostic system and the connected modules may also be possible.

Locating CAN Harness Open Circuits

In the case where multiple modules, including a terminating module, are failing to communicate, having first confirmed the power and ground supplies are correct, the approximate location of the open circuit can be identified from analysis of the Network Integrity test results and reference to the relevant CAN network circuit diagrams. For example, if an open circuit existed in a certain position on the CAN harness, any module positioned on the Network between the J1962 connector and the open circuit should return a response during the Network Integrity test. No responses would be returned from any modules past the open circuit fault in the Network.

CAN Harness 'Spur' Type Configuration Circuits

If, after the initial checks (Network Integrity test using the manufacturer approved diagnostic system, and power and ground supplies to the module have been checked and confirmed as correct), a module that is connected to the CAN harness via a 'spur' type configuration is suspected of not communicating, then the physical integrity of the CAN harness 'spur' can be checked.

This is most easily undertaken by individually checking the continuity of the CAN High and CAN Low lines between the non-communicating module connector (with the module disconnected) and the J1962 diagnostic connector.

'Lost Communications' DTCs

As well as the methods described so far in this document, which can be used to determine the location of an open circuit in the CAN harness, 'Lost Communications' DTCs can also be used for this purpose. Lost communication DTCs mean that a module is not receiving CAN information from another module.

For example, if a global DTC read were to be carried out, only DTCs stored in the modules that the manufacturer approved diagnostic system could communicate with would be displayed. If there was an open circuit fault in a certain position on the CAN harness, the modules that could display DTCs would all be prior to the open circuit on the Network, and these modules should display 'Lost Communications' DTCs with all the modules located on the Network past the open circuit fault.

'Bus off' DTCs

The references to bus and its condition refer to the network concerned and the modules on that network.

If a module logs a 'Bus Off' DTC, it means that the module has detected CAN transmission errors and has disabled its's own CAN transmissions and disconnected itself from the network in an attempt to allow the rest of the network to function. At this point the 'Bus Off' DTC is set. A common cause of 'Bus Off' DTCs can be a short circuit in the CAN network.

Central Junction Box (CJB)

Note. If the control module or a component is suspect and the vehicle remains under manufacturer warranty, refer to the Warranty Policy and Procedures manual, or determine if any prior approval program is in operation, prior to the installation of a new module/component.

Note. Generic scan tools may not read the codes listed, or may read only five digit codes. Match the five digits from the scan tool to the first five digits of the seven digit code listed to identify the fault (the last two digits give extra information read by the manufacturer-approved diagnostic system).

Note. When performing voltage or resistance tests, always use a digital multimeter (DMM) accurate to three decimal places and with a current calibration certificate. When testing resistance, always take the resistance of the DMM leads into account.

Note. Check and rectify basic faults before beginning diagnostic routines involving pinpoint tests.

Note. If DTCs are recorded and, after performing the pinpoint tests, a fault is not present, an intermittent concern may be the cause. Always check for loose connections and corroded terminals.