Doesn't sound right - you should be able to read engine hours etc without the need to run the motor. When you say they "disappear", I assume the data simply starts flashing to show it is invalid - is that correct? Do the gauges still have valid data after it disappears from the NSS12? How is the backbone arranged - is there an isolator in the backbone to separate the gauges from the GPS displays etc? What other devices are in the network?