Dexcom FAQ: What should I do if my Dexcom sensor fails during the 2-hour warmup period?


What should I do if my Dexcom CGM fails during the 2-hour warmup period?


You should first walk through these troubleshooting steps:

  1. Disconnect your old CGM: If you've worn a CGM prior to applying this one, make sure you've ended previous sensor session by selecting Settings > Stop Sensor in your Dexcom app.
  2. Check if the transmitter is fully snapped into the CGM: Make sure the transmitter is fully seated in the CGM cradle by pressing down firmly on the larger end of the transmitter until it clicks into place. You'll know the sensor is fully seated when you hear two clicks and the transmitter sits completely flat within the clear walls of the sensor. 
  3. Wait 20 minutes to see if the issue resolves.

If you continue to receive a Sensor Failed notification, you may have a faulty sensor or the transmitter's serial number was entered incorrectly. Email for a replacement sensor, and carefully follow these instructions to disconnect and remove your CGM: How to Remove your CGM.

After you've removed and disconnected your CGM, check if your transmitter number was entered correctly before starting your new CGM. Here's how:

  1. Open the Dexcom app
  2. Select Transmitter SN in the settings menu (note: this option will not be available once you start a new CGM session).

If you have any questions, please reach out to and we'll be happy to help!

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