CANBUS J1939 Interface
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Description: CANBUS J1939 Interface
Please note that this interface must be powered from a +12V DC supply only.
The CBJ1939 CAN Interface (also known as CAN; CAN-BUS; CAN BUS; C-BUS) is a device for obtaining vehicle speed pulse and engine speed (RPM) mainly in commercial vehicles such as trucks. The unit monitors SAE J1939 CAN Bus for a given message or messages and generates an output corresponding to the equivalent wire loom signal.
The CBJ1939 features built-in diagnostic LEDs to indicate CANBUS status and speed pulse output to aid the installation process. After power-up, only the RED LED will illuminate. At this point, the interface is searching for CAN Bus information. When CAN Bus information is detected, the RED LED will go out and the GREEN LED will illuminate. After this, the GREEN LED will flash according to engine RPM while the RED LED will flash according to vehicle speed.
The CANBUS uses two wires for data transmission. One is called CAN HIGH and the other is called CAN LOW (sometimes marked as 'CAN+' and 'CAN-' respectively). The CANBUS connections on the CANBUS interface should be connected to the appropriate CANBUS connections with an insulated solder joint. Do not cut the CANBUS wires.
IMPORTANT NOTICE: All connections are for guidance only. Vehicle manufacturers can vary wiring from model to model. It is advisable to check the vehicle wiring diagram.
CANBUS J1939 Interface Connections
1. We recommend that the CAN HIGH and CAN LOW connections are picked up from the automatic gearbox ECU where possible, as this has the least amount of data flowing in the system. Note: it is also possible on some vehicles to pick up the CAN wires at the ignition switch, e.g. Mercedes.
2. Because manufacturers continually change the pin configuration of the plugs, it is advisable to pick up +POS and -NEG for powering the interface from an alternative supply, preferably a good ignition controlled regulated supply. A good earth is absolutely essential.
3. Connecting the CANBUS interface close to the ECU, say 5 to 10 cm away from the plug will allow room for the connectors. While the power wires CAN be extended, it is not advisable to extend the CAN HIGH and CAN LOW leads. If there is a need to extend the signal lead (orange), please ensure that it is run to its destination avoiding proximity to equipment that might give off pulses which could be picked up by this wire, such as ignition or heater fans, etc. Common sense tells you that each wire can become an aerial for extraneous signals within a vehicle environment.
4. Note that just because a vehicle has a CANBUS system, it does not necessarily mean that that CANBUS carries speed signal information. Also some vehicles can have more than one CANBUS network and usually only one carries the speed signal information.