Why GPS tracker can't reply SMS command

SMS text command is one of the basic functions for GPS tracker.

The user can send a SMS text command to the GPS tracker and receive a SMS text response from it.

However, sometimes the user can't receive the SMS reply from the GPS tracker.

Below is the guide to check why the GPS tracker doesn't respond to SMS command.

1. Check the GPS tracker's power status.

   If the GPS tracker without exteranl power/Built-in battery supply or in power off status, the GPS tracker can't reply the SMS command.

   
   

   How to know the power status and make sure the device is power on remotely?

   If the device is online in the platform, it means the device is "power on".

   If the device is offline, you can try to call this device. Calling goes well means the device is power on.

   
   

   If the GPS tracker at your hand, just observe the LED light.

   
   

2. Check the SIM card credit

   The users may face the situation that the SMS command can't reply and the GPS tracker device is offline too at the same time. Normally this is caused by the SIM card credit balance reason. You can try to recharge (top-up) the SIM card first and the GPS tracker can resume to work soon.

   
   

   One thing is curious based on our observation, we don't know the reason behind yet. In a few Africa countries, if the SIM card credit runs out, just do the recharging is not enough, the users need press the power key by manual to restart the GPS tracker device too.

   Actually, our GPS tracker has automaically restart mechanism but still not enough in these countries.

   
   

3. SMS command password wrong or incorrect format

   The SMS command format with password, default password is 000000

   For example:

   000000,B00,1,194.135.89.211,10502

   
   

   Some users forgot they have changed the password or use incorrect password to send the SMS command. With incorrect password they can't get the SMS reply.

Below is an exmaple of wrong SMS command format:

000000, B00,1,194.135.89.211,10502

The mistake is "ahead of B00 should not be space after comma".

4. Send to wrong SIM card nubmer

   The GPS tracker works together with a SIM card.

   Normally, the clients need manage many GPS trackers.

   So it is possible the SMS command send to wrong SIM card number.

   Not happened often, but it happens.

   
   

5. Associated with the mobile phone

   For example, in some countries, the Samsung Galaxy S25 ultra model default message APP is not SMS, the users need to download the SMS APP first to use the SMS.

   The mobile phone has message APP which misguided the users but it is not the SMS APP.

   The SMS command can't send out sucessfully due to this reason.

   

   
   
   
   

6. MMS option

   In Austrialia, the mobile phone text message has SMS/MMS options.

   If the users switched to MMS in their phones, it is possible they can't receive the SMS reply.

   Switch back to SMS option, can receive the SMS reply well.

   
   

7. Local network band mangement conflict

   The GPS tracker normally supports pure 2G,4G/2G or 4G/3G/2G depends on models.

   If the GPS tracker is 4G/2G, the common logic is searching for 4G signal first, if can't find 4G, switch to 2G.

   However, in some countries, for example in Brazil, the SMS command seems to be affected by this band switch with unclear reason. We need to lock the band to pure 4G or 2G, then it works. Otherwise the mobile phone can't recieve the SMS command reply.

   
   

8. M2M SIM card

   Some M2M SIM cards can't support the SMS or default settings can't support the SMS before new settings.

   Some M2M SIM cards can support the SMS but must send it from the SIM card manage panel only, can't send the SMS from the mobile phone directly.

   
   

9. In mobile network signal blind zone

   The GPS tracker can't reply the SMS command if in the mobile network signal blind zone.

   It is very difficult to distinguish between the SIM card's credit out and sginal blind zone.

   
   

   You need some extra clues to identify the signal blind zone:

   a) In the same position other GPS tracker works or not?

   b) If the GPS tracker still can't reply the SMS command even keeps moving for long?

   c) Has removed the SIM card credit reason or not?

   
   

   Short to say, you need check the SIM card credit reason first, then consider the signal blind zone reason.