J1939 Terminating Resistors

Mechanics Hub Forums Bus & Coach Thomas J1939 Terminating Resistors

This topic contains 3 replies, has 3 voices, and was last updated by  mike 10 months, 1 week ago.

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  • #25974 Reply

    John Whelan

    I know you truck guys have heard of the Multiplex J1939 system and terminating resistors. we had a problem with one of our C2 (Freightliner Chassis) school buses. The J1939 diagnostic link wasn’t communicating with the ABS module. I did a post and video on what we found wrong with this system. Unhooking the batteries and checking resistance at each module J1939 (green and yellow wires) works for this type of fault. I also want to add don’t count out a bad wire as well. There was another bus with the same problem which ended up to be no continuity at one of the harness plugs.

    #29255 Reply

    Hi John.
    I am not a truck guy but AG and Construction equipment uses the J1939 Can system as well. In the past most systems used two or three external terminators on the can bus. Those terminators are typically 120 ohms, which means the can resistance is 60 ohm (2 terminators) or 40 ohm (3 terminators). Our newer equipment mainly uses terminators that are integrated in a controller or module. Instead of replacing just the terminator, you have to replace the complete module.
    An other common cause of a “no communication” problem can be a faulty controller on the can bus. In this case you have to unplug one controller at a time until you find the faulty one. Not too complicated.

    #29256 Reply

    John Whelan

    Thanks for the info Andy! Multiplexing seems to be everywhere 🙂 I’ve heard that several OEMs have the resistors in the modules which means changing them out as you have experienced. The terminating resistor on the Bus I’m working on costs under 15$. I hope they keep them external in this case. I can see it being an advantage having them inside a module to protect them from the elements.

    #49999 Reply



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