Network operator issues - in this case contact network operator and ask if there are no issues on their end. Please refer to THIS page to see how to contact operators support.

Device has no (too low) power supply - check the last known power supply value in TT2. All of our devices have power voltage ranges in which they work. Exact values can be found in the documentation of the devices. For example HCV5 needs at least 9V to work. Meaning if the supply is lover than that, the device is likely not to work. Light vehicles normally need to have batteries with at least ~12V. So if the device does not work, there is virtually no way the vehicle will start. Inform the client about a dead battery.

Device is broken - if the device does not have any LEDs flashing even when power supply is above 10V preferably 12V, the device is likely to be broken. Only RMA process at that point.