ButDoISay

A Science Guy's Life on the Medtronic MiniMed 670G Insulin Pump and More.

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Category: CGM Sensors

RECOVERING FROM THE “SENSOR UPDATING” message

You get this dreaded message on your Medtronic MiniMed 670G:

Do not Calibrate. Sensor Updating.”

You know that chances this will mean that you have to replace your all-valuable sensor when it is all said and done. I have not had so much luck with the “updating” part. Almost always the story ends with “replace sensor.”

In most cases the sensor updating message comes on because I have entered consecutive meter BG readings that the sensor does not like.

What i do when i get the “sensor updating” message

To salvage my current sensor this is what I do:

  1. Very carefully remove the tape and completely disconnect the transmitter.
  2. Charge the transmitter once again.
  3. Turn-off the sensor option under Options>Utilities>Sensor Settings.
  4. Remove the transmitter from the charger.
  5. Turn-on the sensor option under Options>Utilities>Sensor Settings.
  6. Reinsert the sensor and start a new connection and go through warmup under
    Options>Utilities>Sensor Settings>Sensor Connection>Start New Sensor.

morning fasting glucose not exactly where i want them to be

As you can see my morning fasting glucose numbers are running higher than I would like them. I feel well rested in the morning if my numbers are below 120. Above that I wake up feeling tired. I have also noticed that it is in the morning that I get the biggest differences in reading between the Minimed 670G pump Guardian sensor and my BG meter (during other times the readings are within 10 mg/dL of each other but in the morning closer to 20 mg/dL ). Not sure why the sensor consistently under-reports my BG readings, but it is at this time that I would love my sensor to be the most accurate! Most probably it might have to do with the fact that the Auto Mode algorithm is likely most conservative at night.

Upper Thigh Sensor Insertion Sites ARE more accurate than belly sites

Bottom-line: For accuracy and fewer calibration errors I have found upper thigh sensor insertion sites better than belly sites. These sites take longer to stabilize (about 12-24 hours) but always give me very good accuracy and fewer calibration errors over the life of the sensor. Sensor values seem to match better with meter values for the upper thigh sites over the belly sites.


During my pump training, I was told that Medtronic now officially recognizes the outer side of the upper thigh as an FDA approved insertion site for the Guardian sensor. This was not the case for the Enlite sensor.

To shorten the time it will take the sensor to stabilize and enter Auto Mode, some people suggest inserting a new sensor and leave it in place a couple hours prior to replacing the current sensor. I have had mixed results with this approach with some sensors dying when it comes time to insert the transmitter.

Kicked Out of Auto Mode….Again!

Guardian Sensor Stability and Auto Mode

I have been trying to get back to Auto Mode for the better part of the day today.

As you can see my readings in manual mode were not so bad and I would say those were stable sensor readings. I am not sure what reading variance the Auto Mode algorithm considers acceptable to enter Auto Mode.

Variance does not look too shabby but Auto Mode did not like it.

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How Do Guardian/Enlite CGM Sensors Work?

Continuous Glucose Monitor

Continuous Glucose Monitoring (CGM) sensors are finicky, expensive and we all know of how much of a process it is for Medtronic to replace faulty sensors. For me, changing Medtronic CGM sensors is a ritual I do not look forward for many reasons. Getting my sensor inserted and working correctly seems to be a hit-or-miss proposition.

But the delicate nature of sensors is due to the fact they are miniature electrodes that are affected by small changes in the environment around them including small movements or presence of interfering chemical substances.

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