Information Bus: Testing and Inspection
isInspection and Verification
CAUTION: Diagnosis by substitution from a donor vehicle is NOT acceptable. Substitution of control modules does not guarantee confirmation of a fault, and may also cause additional faults in the vehicle being tested and/or the donor vehicle.
NOTE:
Check and rectify basic faults before beginning diagnostic routines involving pinpoint tests.
1 Verify the customer concern.
2 Visually inspect for obvious signs of damage and system integrity.
3 If an obvious cause for an observed or reported concern is found, correct the cause (if possible) before proceeding to the next step.
4 If the cause is not visually evident, check for Diagnostic Trouble Codes (DTCs) and refer to the DTC Index.
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 this article. For additional 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.
Media oriented systems transport (MOST) diagnosis
Overview
The basic guidelines are covered in the description and operation section, such as not attempting to repair fibre optic cables, but additional precautions include:
- Do not touch the exposed ends of the optical fibres (grease from skin can contaminate the fibre)
- Whenever the fibre optic cable is disconnected, cover the connectors to prevent dust contamination
- Do not expose the fibre optic cable to heat
- Do not bend the fibre optic cable through less than a 25 mm (one inch) radius
- Do not use laser pens to test the fibre optic cable's ability to pass light
- There is a dedicated tester to use with the MOST network modules and fibre optic harness to assist with diagnosis and to test the fibre optic cable's ability to pass light
MOST tester
Before connecting the tester to the network, turn on the unit and check that the red power on indicator is illuminated.
If not, the battery should be replaced before using the tester.
2+0 Self-test
1 Set the connector selector switch to 2+0.
2 Select beep or LED on the tester, depending on your choice of indicator.
3 Turn the tester on and check the operation of the power indicator.
4 Using the 2+0 loop-back lead from the kit, push it into the 2+0 connector housing in the tester until it clicks into place.
5 Press the red test button in the center of the tester.
6 Depending on your choice in step 2, the tester will give either an audible tone or a green light.
- If the tester continues to give a tone or light after the test button is released this does not indicate a fault, only that there is a signal feed-back within the tester which will stop when the loop-back lead is removed.
2+4 Self-test
Carry out the self-test in the same way as for 2+0, but using the 2+4 loop-back lead and select 2+4 on the connector selector switch.
Vehicle diagnosis
CAUTION: Make sure the tester is not connected to the MOST network when either switching the tester on or switching between 2+0 and 2+4, as the tester emits a brief pulse of light which could introduce a fault into the network.
7 Use the approved diagnostic system or a scan tool to retrieve any DTCs.
8 Set the connector selector switch to 2+0.
9 Disconnect the intermediate fibre optic cable connector and connect the male half to the tester connector at the top of the unit using the adaptor in the kit.
10 Turn the tester on and check the operation of the power indicator.
11 Set the LED/beep selector to LED.
12 Turn the ignition switch to the ON position.
13 If the green LED is active, a signal has been received indicating that the first half of the optical ring is functioning.
14 If the green LED is NOT active, no signal has been received indicating that the first half of the optical ring is NOT functioning.
- A ring break code should be set as a result of this. Use the approved diagnostic system to trace the fault and clear the code.