Quote:
Originally Posted by SwissXC90
A can bus is terminated in 2x120 ohm resistors
If both terminations are present, you measure 120/2=60 ohms
If one termination is disconnected, you measure 120 ohms
If both terminations are disconnected, you measure open circuit.
This is a simple way to test if the terminating devices are plugged in.
It is purely a passive test. It does not confirm if can bus data is ok
The can bus is very robust and will continue to work under almost any failure scenario.
So one or two terminating devices missing will not kill the bus.
The other passive test is to check can high and can low resistance to ground. Neither should be connected to ground, or to 12V.
If the CEM is refusing to communicate, then check
Power to CEM
CEM ground
CEM can bus connection
CEM Odbii can bus connection.
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In addition you can measure DC voltage on the 2 CAN wires , the low should be around 2.2v and the High 2.8 v depending on activity on the network .