The BUS is the digital data communication system that connects the powertrain controller, transmission controller, body computer, anti-lock brake, indstrument cluster, etc systems together to share information needed to run the vehicle. Because there is no number associated with the "no bus", I can't be sure exactly what is wrong with that system. Usually there should be a 4-digit number as the fault code, not just a "no bus". I would suggest that you go to either an Autozone Parts store to get a readout using a code reader, or to a shop to have the readout of the bus system. Autozone will often do the readout for free. If you get a 4 digit number of another message let me know what it is. I suspect that because the engine shuts down that the engine (powertrain) controller has failed as regards its ability to send/receive data necessary to run the vehicle. But a regular readout with a code reader is probably your best action.
Roland