J1939 ,9pin Deutsch diagnostic connector
You are correct that the resistance between CAN Hi and Low should be 60 ohms.  Each end of the bus should have a 120 ohm resistor, and since there should be only 2, their parallel resistance should be 60 ohms.
Have you made sure you are measuring resistance across the correct pins on your diagnostic connector?  I believe this is the connector you have:



So make sure the resistance between C an D (CAN Hi and Lo for j1939 bus) is 60 ohms.  If it really is much lower, there is an electrical problem.  Your CAN bus may be frayed somewhere and shorting to Ground or something.  CAN communication relies on having the correct resistance between CAN Hi and Lo so it's likely your j1939 bus won't work until you get that issue resolved.