When not to stop an expiring Dexcom sensor

I recently ruined a Dexcom G6 sensor. I think I know where I went wrong.
Dexcom customer service didn’t agree with me, though, and I wanted to check if anyone else has had this experience or has an alternate theory about it and also to warn others not to do what I did.
My sensor session was expiring at 1:31 and at 1:29 I decided to stop my sensor from my Tandem pump and put in a new sensor and started the sensor with the sensor code. The pump showed the little warm up circle and all seemed fine.
But then my iphone sent me a message that my sensor had expired. I ignored it. Maybe 20 minutes later I looked at my tandem pump to see how the warm up was going and I saw that there was no warm up (just a red x where the warm up pie would be) and now the pump said my sensor session had ended and asked me to start a new sensor. I went ahead with start new sensor (entering the code) and then the pump said that I could not reuse a sensor (which, to be clear, I was not trying to do. Just trying to start the warm up on what was a new sensor.)
My theory on this is I just should have waited two minutes and let the darn thing expire before putting in a new sensor!
Not much harm was done since Dexcom customer service sent me a replacement sensor.
The thing that I’m slightly confused about, though, is that customer service said that I had followed the right procedure (stopping the previous session on the pump and starting a new session on the pump) and the fact that I had done it so close to the time the sensor was expiring should not have caused a problem so the problem was that it was a bad sensor. I suppose this is all sort of academic at this point, except that I will not be so impatient in the future and will either end a session at least 10 or 15 minutes before the sensor is about to expire or I will let the sensor expire before staring a new session. I’m pretty convinced that I messed things up by ending a session within the little 5 minute window between when the pump communicated a blood sugar to the iphone and the sensor expiration time. Don’t know if anyone else has managed this little trick of how to ruin a sensor. But, I think I’ve managed to invent one more strange little way that things can go wrong and, of course, it would have been quite upsetting if it had been my last sensor of my 90-day supply.

How long did you wait between ending the sensor session and starting up the new sensor? If you didn’t give the Dexcom app on your phone enough time to catch up to what you did on your pump then when the Dexcom expired on the Dexcom app then it may have ended your sensor on the pump.


That’s right, you have to wait 15 to 20 minutes after stopping a sensor before you start a new one. It is most important if the old sensor code is the same as the new sensor. I frequently stop my sensors before they expire simply for my own convenience in replacing them. I always wait at least 15 minutes before activating the new sensor. Never a problem.


Interesting, I’ve never done this and haven’t had an
issue starting new sensors. Is this a Dexcom instructed step?

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I would suggest you look in your pump history and see what sensor code was used to start the previous sensor and the one that failed. I suspect it was the same code.

Great icon > history > cgm history > sessions and calibrations > find the dates the sensors in question were started>

A while back, Dexcom made a software change to prevent restarts. But then all of a sudden people were getting lots of failed sensors. So they came out and gave us the workaround, and advised everyone wait 15 minutes between sessions to purge the transmitter’s memory of the previous sensor. Lo and behold, no more “no restarts allowed” and you CAN indeed restart old sensors. Apparently the software change just forbids you from starting two consecutive sessions with the same code, without waiting 15 minutes.

If you’ve got different codes, you should be fine to start the next session right up, but I would make sure to stop the season on both devices first to avoid any confusion.


Yes, this is part of Dexcom’s instructions. They also instruct to wipe the transmitter with alcohol before reinserting into a new sensor. This cleans off the contacts. I don’t think many do that either and may incur problems as a consequence.

I have had Dexcom tech support advise me of this after a similar experience. I believe it was the same sensor code. I do not use a tandem pump. I just use the G6 app on my phone. I now wait 15 minutes between sensor changes and have not had the problem reoccur.

It was incredibly annoying because I use Skin-tac for my Dexcom sensor sites which makes them incredibly difficult and unpleasant to peel off right after putting them on- even with uni-solve.

There are a couple of things that make a difference that I didn’t know until recently.

I never have an issue starting a sensor immediately after the old one expires even with the same code.

When you insert a new sensor the readings are super high. Thats part of the reason the values are blocked for 2 hours.

But the program expects to see this high reading ,and if your readings are too low, it assumes you tried to restart the sensor.

So they instruct you to wait 15 min until the memory buffer is empty before you start the sensor just in case.

When you remove the transmitter, it will do a hard reset if the memory buffer is empty. So that is how we are able to restart them by taking off the transmitter, waiting and then reinserting it.

But if the initial readings are too low, it figures you are restarting it and will give you a failure message anyway.

This is why my method of re-pairing the transmitter instead of removing it will work but only if the sensor is still giving a relatively strong signal.( I don’t know the threshold) but I know it drops off the longer you wear it and the hexonase reagent is used up.

That being said, if your sugar is running high, you will have a better chance of restarting it no matter what method you use.

And yes this is why they tell you not to start a sensor until you are in therapeutic range.

I think the best method to restart is to put a test strip up under the transmitter and leave it there for 15 min blocking the contacts. So you get that hard restart without removing the transmitter.

I didn’t come up with that method, but I’ve seen it on various forums, and I tried it just to see if it would work.


Interesting, never experienced those issues with the sensor, but good to know.

My biggest issue was accuracy in the first 8 hours, but was resolved after moving the placement from my abdomen to the arm. Now pretty much spot on out of the gate.


I’ve had a couple of sensors that gave really goofy readings just after startup. I “reset” the sensors by restarting and all was good. If I ever encounter what you experienced, I will try a restart.

That’s the most detailed explanation I’ve seen of how the sequence actually works—thanks! I’m curious where you got the info, since Dexcom is pretty close-mouthed about this stuff.

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Timothy – is there a way to check that you’ve successfully blocked the Dexcom transmitter contacts with a test strip?

I sometimes restart a sensor once, and I first stop the sensor, use 2 test strips from both sides to pop out the transmitter, then wait 15-30 minutes, etc. But blocking the contacts without removing the transmitter sounds easier.

If you have successfully blocked the contacts you will not get a reading. Wait 5 minutes. I just tried this with my wife’s expiring sensor. The test strip I had seemed too thick to slide in. So I took it off and figured out what needed to be done for next time. It will work if you have something thin. It is a great idea.

So yes I got the sequence from a schematic flowchart from the initial plan for the g6 before they actually built them. And before they really worked out the bugs. I got that schematic from an engineer who works for a competitor who I’m not going to name.
The whole reason was to prevent restarts. A requirement to get FDA approval for no calibration use. And they used the reality of a strong initial signal to their benefit. It wasn’t to make more money even though it achieved that too. At least that what the schematic said.

If you put the strip in from the narrow edge straight under. It will block both contacts. Wait for your pump or phone ap to miss a reading. So you might want to do this before the sensor session expires until you get used to doing it.


I too have never waited to stop a sensor and start a new one. I do however clean the contacts on the Tx.
Another step that should be done , is when you remove the old sensor for pease of mind , verify that the sensor wire is still attached. Once I had one break off , but was fortunate enough to have it exposed above the skin enough for me to grab it with tweezers . Some people like to “pre soak” there sensor by inserting before had. As far as I’m concerned it’s a waste of time as you still have the two hr warm when you start the new one

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I presoak for 12 hours. When my warm up is finished my numbers are spot on.

Everyone is a little different. It’s not skin off my nose to put the sensor in before I need it, and I avoid those hours of inconsistent numbers

You are absolutely right!! I use an Android phone, and I have to wait until I get notification from my phone that the old sensor quit and to start a new sensor.

A link to explaining the different methods of restarts. The first video talks about blocking the signal with a test strip. I’ve done it and it works. Although it’s just as easy for me to pop out the transmitter with a guitar pick.

Tony24, were you going to share “what needed to be done,” or a share your method with those who’ve not figured out how to remove transmitters?

Apparently my OneTouch blue test strips are not ones others use to do this, because they are too thick to pry the transmitter from the sensor.

And, can I guess you’re talking about sliding the test strip in from the wide end of the transmitter? How in the world can you do that without having pried the transmitter from the sensor?

If anyone has a link to a video, I’m appreciate seeing it, thanks.

Slide the strip in the slot on the NARROW end of the transmitter. You need someone else to do it If on arm. I just did it the other day with the sensor on my wife’s arm. Sand the end of the strip with a emory board or what ever to get rid of some thickness to make it easier. stop sensor, insert strip, wait 20 mins. I will post a pic tomorrow afternoon.