I am making a CAN logger device that will be connected to the vehicle OBD port. Since the CAN bus inside the vehicle is already terminated, do I need to terminate the BUS lines on my device end, right before the line feeds to the CAN Transceiver? Please check the attached picture. The J1939+ and 1939- are the BUS lines available on the Vehicle OBD port. I have read that if the stub lines are not too long(<0.5m) , termination is not needed. The stub lines in my case is much less than 0.5m.

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  • \$\begingroup\$ Depends on if there is termination in the other end of those signals or not. You should ensure that resistance between CANH and CANL is roughly 60 ohm and that's about it. \$\endgroup\$
    – Lundin
    Dec 6, 2019 at 11:30

1 Answer 1


No. You only need to keep the stub length below the specification for the bitrate.
Which according to j1939-14 (4.2.1) is a maximum of 1.67 meters.


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