It article describes how missing CAN bus termination causes signal distortion, leading the device to detect a “bus off” error condition.
Ixxat Mobilizer, Ixxat CANnector
Why do I get a bus-off when the CAN-FD ports are not connected?
When a bit is sent to a port to which no CAN cable (and therefore no device) and no bus termination resistor are connected, the device signals "bus off". This is due to the lack of termination in this case, which shortens the transmitted recessive bit so much that the device can no longer recognize it as such. The problem does not occur with correct termination.
