What drives the actual can high and low

so one point I seem to be missing is where does the actual base can voltage come from? I mean I understand the can trunk is 2 twisted wires with a terminating resistor at each end, but it also has a voltage on it. Where does that come from?I mean 2 wires don’t just have a voltage on them, lol! Do all the nodes connected to the trunk actually drive the base can high/low voltage or is there a specific device and if that goes faulty the entire bus dies?

Each device pulls the CAN High signal high with a weak resistor (I'm sure it's detailed in the spec), and the CAN Lo signal is pulled low with a weak resistor. When CAN Hi > CAN Lo it indicates the bus is in the idle state. Any device can start to transmit on the bus, and if the state of each bit doesn't match what they are transmitting, then they have to backoff and allow another transmitting device to continue sending the packet. Because of this, low CAN IDs (aka CAN Addresses), get priority as any higher address would find that the attempted transmission of one bit is received as a zero and would back off.

Now what can kill the bus is devices that aren't using the same bus speed (aka baud rate). All devices need to be communicating at the same bit speed for the protocol to work. Some devices will detect a high number of errors and stop transmitting themselves so the bus might continue to function if they are the one with the wrong bus speed.

Another thing that can kill the bus is too much termination. Termination (a resistor between CAN Hi and CAN Lo signals) adds load to the but, and the more there are in parallel, the lower the effective resistance and the more drive current is required. Some devices can't drive the bus with sufficient current, and so they don't work. Per the spec, the bus should have just two termination (one at each end of the bus) typically 100 - 120 ohms each. Measuring the resistance on the bus (when not powered), should yield 50 - 100 ohms for a working bus. Many aftermarket devices have termination built into them, and you need to remove a resistor or cut a trace for them to work in a more complicated CAN network with many devices.