Problem on the CAN Bus system
Here I have a problem with my High and Low Speed CAN bus and this stop me from starting the car...
I really need help.
On the diagnostic socket (OBDII) on the yellow and black wire, PIN 14 (Low Speed CAN bus) the voltage is only 1.3V but on yellow and brown wire, PIN 6 (High Speed CAN bus) the voltage is ok at 2.5V.
I have read that if I have a problem on the BUS system (module not working properly) the voltage would be too high, around 7.0 V but I have not found anywhere the reason why the voltage could be too low....
At the same time when I remove the battery and check the Resistance, between the PIN 3 and 11 it's ok I have 60 Ohms but again between the PIN 6 and PIN 14 I have 120 Ohms, this result confirm that I have a problem...
Please, can someone guide me where to search the problem ?
If I'm wrond somewhere please tell me too !!!!
Thank you so much in advance
Down I attach what I have found about the CAN bus system, it's long but it can be helpful for someone else....
Discovery 3 OBD II connector, Pin 11 CAN Low, Pin 3 CAN High Or, Pin 14 CAN Low, Pin 6 CAN High
Yellow/Black CAN Low Yellow/Brown CAN High using a multi meter + to the pin - to earth the reading will be 2.5 Volts
If the voltages are excessive, for example CAN High is reading 7.0 Volts, then remove the suspect module by disconnecting it and see if the voltage returns to 2.5 Volts if it does then, the problem is solved
Obviously the voltage will fluctuate when reading
Two CAN busses are employed on the vehicle:
* Medium speed
* High speed
The medium speed bus connects the following control modules:
* Integrated Head Unit (IHU) or low line head unit
* Heating and ventilation control module
* Fuel burning heater
* Park distance control
* Tyre pressure monitoring control module
* Central junction box
The high speed bus connects the following control modules:
* Steering angle sensor
* Air suspension
* Electric park brake
* Electronic rear differential control module
* Terrain Response™
* Restraint control module
* Engine control module
* Transmission control module
* Adaptive front lighting system control module
* Antilock Braking System (ABS) control module
IDS Vehicle Integrity Test
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.
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.