What is J1939 data link?
J1939 is a high-speed vehicle data link that can communicate at either 250kb/s or 500kb/s. The datalink consists of three wires: yellow is CAN +, green is CAN – and Shield is connected to ground.
CAN termination resistance?
CAN Bus Termination. There should be a 120-ohm termination resistor located at each end of the bus to prevent signal reflections. When you measure the resistance between CAN HI to CAN LOW on a wiring harness you should measure 60 ohms. This measurement should be conducted with the device power off.
Why is a termination resistor needed?
Purpose of the Terminating Resistor A Terminating Resistor is a Signal Quality component. It is used to soak up an AC signal, preventing reflections or ghosts on the line. It takes time for signals to travel along wire, and the energy of the signal cannot be created or destroyed; it has to go somewhere.
Are there any inactive codes for ABS J1939?
Trucks will come into the shops all the time with inactive codes for data links, such as ABS J1939 time outs, communication errors, and Engine ECU’s data link failures. Most of the time these codes will get erased and minimal or no troubleshooting will be done.
When to check the J1939 on pins C and D?
When checking the J1939 on pins C and D make sure the ignition is off and no modules are communicating when you check the resistance. What I see all the time are inactive codes in the ABS for J1939 time outs on Freightliner Columbia.
Is there a problem with the J1939 data link?
In most data link troubleshooting text books this is an acceptable measurement and falls within the 60 ohms + or – 10 ohms. My experience tells me there is a problem in the J1939 data link. Before I get into actual troubleshooting you will need to understand how to calculate the resistance in the J1939 harness.
Where are the electrical connectors in a 379?
LOCATIONS OF MAJOR ELECTRICAL MODULES IN 379E CAB AND SLEEPER TURNSTALK MODULE FIREWALL CONNECTOR – HOOD AND TRAILER HARNESS FIREWALL CONNECTOR – ENGINE AND CHASSIS HARNESS ENGINE HARNESS FIREWALL CONNECTOR ABS HARNESS FIREWALL CONNECTOR LOCATION OF MAJOR COMPONENTS Schematic – 379 Model Family Electrical P94-6023 C 03