Its your med speed can network that's going down. You can find a lot of info about how can networks work. Some network issues can be pretty simple , sometimes not so much. It's going to come down to making some measurements on the network and reading vehicle faults to figure out what modules are not responding. Your mostly going to be looking for other modules saying they lost coms to your problem module. The modules can be not turned on because of a loss of battery voltage or it could be awake but the network wires are either broken or shorted.
The med speed is at terminals 3 and 11 on the diagnostic connector. I measure the voltage on the network first with the key on or running better still. You should have pretty close to 2.6 volts on term. 3 and a little less on term. 11 like 2.3. If that's ok then I shut it off and disconnect the pos. battery cable and measure resistance from 3 to 11, then from each of those to ground. You want to see 60 ohms between 3 and 11. You should see about 2K to 3K ohms to ground.
