Machine comms troubleshooting
The most frequent issues you will find while troubleshooting communication buses are:

-Hardware: cables not connected correctly (number one when you have multiple pin connectors like your case) or the wrong type of cable (impedance not correct) or there is no termination when it should be.

-Configuration: Different settings on either side, like baudrates or protocols.

For your CAN bus network in particular, you don't give much information on the tools you are using and trying to diagnose based on bus voltages only is quite difficult. 

My advice is to follow one of these routes:

-Get yourself an oscilloscope and look at the signals on the bus. Even if you don't have experience you can find a lot of resources online. This is a good starting point. 

-Switch off the power of all devices on the network and take a look at resistances. See, for instance, a short guide here.

-Check both sides of the communication bus independently. If you're using an OBD cable test it somewhere else (for instance another car that you know was working properly or a dummy testing device). If you don't have additional tools this might seem difficult or expensive but nowadays you can get very cheap hardware and you would save a lot of time. Better to have more devices and tools than you need than waste hours or days hitting a wall.

-Edit your question with more details. What OBD cable you have? Have you been able to make it work somewhere? What software are you using? What car or CAN device are you trying to connect to? What other resources you have available or you might be able to get?