FMC234 loses GNSS fix when GLONASS, Galileo, or BeiDou is enabled, but works correctly with GPS only

Telematics Issue
1

Hello,

I have a Teltonika FMC234 running the latest available firmware version, 04.00.00.Rev.13, and I am experiencing problems with the GNSS signal.

During the initial tests performed in a vehicle, I noticed numerous sudden position jumps on the server where I receive the telemetry data. It seemed as though the device was losing its position fix and continued reporting the last known position for some time.

Initially, I had configured the GNSS combination that, in theory, should provide the best accuracy in my area, Spain:

GPS + GLONASS + Galileo

After the device had been powered on for a while, I would normally see approximately:

  • Between 7 and 9 GPS satellites
  • Between 7 and 8 GLONASS satellites
  • Between 1 and 3 Galileo satellites

The problem is that, although the satellites appeared as visible, the number of satellites in use was usually zero. Whenever any of them changed to “in use,” they would remain in that state for only about one second, which is approximately one update cycle in the application. The device would acquire the satellite and immediately lose it again, or at least that is the behavior shown in Teltonika Configurator.

I also found it unusual that, despite having a higher number of GPS satellites available, the device seemed to be trying to obtain its position mainly through GLONASS. I understand that the receiver may internally select the satellites with the best signal quality or strength, but I do not understand why it appears to prioritize GLONASS when more GPS satellites are available.

By chance, during one of the tests, I configured the device to use GPS only. At that point, it obtained a stable position and stopped losing the fix. The satellites remained continuously in use, and the reported location was correct and stable.

However, when I enabled any of the following combinations, the problem returned:

  • GPS + GLONASS
  • GPS + GLONASS + Galileo
  • GPS + BeiDou

With any of these configurations, the device once again had difficulty obtaining and maintaining a stable GNSS fix.

I have also observed another unusual behavior. Sometimes, after changing the GNSS mode, the change does not appear to be applied correctly. For example, the device sometimes continues to display or use GLONASS satellites even when it is configured for GPS only or GPS + BeiDou. Satellites from other constellations that should theoretically be disabled also continue to appear as visible.

I have even restarted the device with only the GPS constellation enabled, but after startup, Teltonika Configurator once again shows both GPS and GLONASS satellites. I do not understand whether this means that the configuration is not being applied correctly, whether the module continues to detect other constellations even when they are disabled, or whether this is simply an issue with how the information is displayed in Teltonika Configurator.

This image was taken immediately after powering on the device. As shown, although the device is configured to use GPS only, Teltonika Configurator displays both GPS and GLONASS satellites. In this state, the device is unable to obtain a position fix.

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This image was taken immediately after the first one. Without restarting the device, I enabled GLONASS and then disabled it again, leaving only GPS selected. After making this change, the device successfully obtained a position fix, as shown in the image.

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All tests were performed under the following conditions:

  • Outdoors
  • With a completely unobstructed view of the sky
  • With the device installed in the orientation recommended by the manufacturer, with the logo facing upward as indicated in the manual
  • A-GPS enabled
  • A-GPS updates configured every six hours
  • All power-saving modes disabled

Initially, I thought that the device might be defective or that there could be a problem with the GNSS antenna. However, after performing numerous tests using GPS only, the device worked perfectly. Even after returning from a test route and entering a garage, the device continued receiving satellite signals.

So far, I have carried out the following actions:

  • Restored the device to factory settings
  • Reinstalled the firmware in case the previous installation was corrupted
  • Tested different GNSS constellation combinations
  • Saved the configuration and restarted the device after changing the GNSS mode
  • Reviewed all the information available in Teltonika Configurator
  • Attempted to analyze the dump files to determine whether I could extract any useful information from them
  • Performed outdoor tests with the vehicle both stationary and in motion

Despite all these steps, the behavior has not changed. The information provided by Teltonika Configurator has not allowed me to investigate the issue any further, and I have also been unable to draw any clear conclusions from the dump files.

Has anyone experienced a similar problem with this model or this firmware version?

Is there any way to determine whether the problem is caused by the firmware, the configuration, or the GNSS module itself? I would also appreciate any advice regarding which logs, parameters, or files I should review to obtain more detailed diagnostic information.

Thank you in advance.

2

Good Day,

Thank you for the detailed description and for outlining the troubleshooting already performed.

The GNSS combinations you tested—GPS only, GPS + GLONASS, GPS + GLONASS + Galileo, and GPS + BeiDou—are supported by the FMC234. Therefore, the issue cannot be explained simply by selecting an unsupported combination.

Based on your observations, the loss of fix with multiple constellations and recovery after toggling GLONASS warrant investigation into how the GNSS configuration is applied during startup. However, this does not yet confirm a firmware defect or exclude a GNSS module issue.

Satellites being displayed as visible does not necessarily mean they are being used to calculate the position. Similarly, the satellite counts alone do not establish that the receiver is prioritising GLONASS. We would need diagnostic logs to determine whether the unexpected constellation information reflects the module’s actual state or a Configurator reporting issue.

Please submit the logs, configuration files, and device IMEI on a Partner Portal ticket. Please contact your sales manager if you do not have access to the Partner Portal. If another FMC234 is available, testing it with the same firmware and configuration would also help establish whether the issue is specific to this unit.

For now, GPS only can serve as a temporary workaround, provided you verify that the fix remains stable after restarting. The root cause will need to be confirmed from the diagnostic data.

Best regards,
Imran S.

3

Hello Imran,

Thank you very much for your reply. I was waiting for the seller to respond so that they could open a support ticket, but I have not received a response. Is there an alternative way to send you the test results and diagnostic files so that a technical support engineer can review my case?

I have carried out further tests, and the behavior has worsened. The device now also struggles to obtain and maintain a position fix when using GPS only. Enabling GLONASS and then disabling it again, which previously allowed the device to obtain a stable fix, no longer works reliably. As the problem persisted, I restored the factory settings and repeated the tests, but the device still fails in the same way.

I also performed the restart test you suggested: with the device in an open field and a valid GPS position fix, restarting it without changing the configuration causes it to stop obtaining a position fix.

Unfortunately, I do not have another FMC234 available for comparison. I purchased this unit to evaluate whether it would be suitable for replacing the devices in my fleet, but I have postponed purchasing additional units because of these issues.

Regarding the visible satellites, I understand your clarification: appearing on the screen does not necessarily mean they are being used to calculate the position. My initial interpretation was based on observing that, whenever satellites from other constellations appeared, the device stopped maintaining its fix. I am reporting this as an observation, not as a conclusion about its internal operation.

I am willing to carry out any tests you consider necessary. Could you please provide a specific procedure for collecting the logs? For example, how long should I leave the device powered on, which constellation combinations should I test, and at what point should I generate the dump files?

I would also appreciate instructions on how to send you the IMEI, configuration, and diagnostic files privately, given that the seller is not responding and I do not have access to the Partner Portal.

Thank you very much for your assistance.

Best regards