check the LED indicators are OK, if not, you can check the SIM card following next steps:
1.call the SIM card of the terminal and check if you can hear the connect ring.
2.Check if the vehicle is in the area where there is no GSM signal.
3.Check if one terminal or all terminals are offline in the area . If all terminals are offline, you should ask the network operator. If the network is OK.
4.Check if the SIM card has enough balance.
5.If the terminal becomes offline on the last day of one month, please check if GPRS is close.
6.Inquiry the parameters of terminal via commands and check the accuracy of the parameters.
