Can Dexcom sensor restart after a "Failed Sensor" Error?

Hi. Now it’s our turn for problems. Had repeated ???, sensor Error 1 and Sensor Error 0 on sixth day of our working sensor. Restarted at least three times. Gave up. We then inserted a new transmitter (Dex tech said we had a transmitter problem and mailed us a new transmitter), along with a new sensor. After startup and double calibration, Dex immediately reverted to ??? Restarted sensor. Sis picked up where I left off and reported a “sensor failure” error. I have never had this error. She restarted sensor. Guess we will all know if it works later today, but if you “stop sensor,” then “restart sensor,” as a fix, does anyone know if this fix works on Failed Sensors? I am guessing you might have to pull the sensor?

From what I’ve read it sometimes works… sometimes fails again. You won’t know until you try it I suppose.

Thanks for the quick response! Waiting with baited breath. Time will tell…

We used the dexcom for a while. We would get ??? when my son’s Blood sugars were fluctuating rapidly. Even after a restart. It would have a hard time picking him up. After a while it would give up and come up with XXX. I don’t believe you can start again after that.

Hope you have luck with it.


In my experience, it’s almost always a “fatal” problem. But during the first day, I would give it a second chance. Just ONE second chance, then a new Sensor.

Here’s something which you should do on Monday: Plug in your receiver and download the data, call up support, and send it in for analysis. Although the receiver decided to say “???”, rather than show a number, it does have the raw data recorded- and that will show WHY it sputtered with “???” before dying, as well as why it declared “Sensor failure”.

As you already know, Dexcom usually follows rising bG with much more delay than it follows dropping bG. An initial calibration during a period of strong rise may be impossible for the calibration formula to correlate with later calibrations done at level or falling bG. And, with only a couple of extremely conflicted numbers to work from, it gives up.

One tactic, if it’s not equipment failure: watch the 2-hour “countdown” graph closely, and be sure to take a fingerstick bG about 15-20 minutes before the startup calibrations will be requested. Then, if your first calibration fingerstick is more than about 1 mg/dL per minute higher, simply don’t do the startup using that finger poke: Ignore the Dexcom’s nagging and just wait for the rate of “rise” in the fingerstick values to level off before entering the startup calibration values.

A “full” restart avoids the nagging beeps, but requires you to wait for a full two hours.

Thanks, Rick! You really do know all when it comes to Dexcom. As it turned out, Dex DID decide to work and it worked well until early a.m. when Sis noticed the numbers were really off. She just calibrated and Dex would come back into range. This morning, she had a High alarm, but DN in range in the low 100s. Calibrated Dex, and Dex came back into range. Then two hours later, a Low alarm. Rinse and Repeat, LOL. Now this is on a brand new transmitter. I know Dexcom appears to be having issues with a lot of their sensors. Would I be remiss in surmising that it is really the RECEIVER that is off? I am guessing this because Dex failed early on a nice working sensor. Sis used sensor from new box with brand new transmitter and we are having issues. We have not had stellar performance from Dex’s inception, but we don’t expect perfection; we know Dex is having problems, we will take the good with the bad. We know the issues will be resolved. In the meantime, sometimes we get 60 percent good readings, sometimes 40 percent. Better than nothing. And we are thrilled she does not mind wearing Dex and seems to kind of like it. I say “kind of”, not say she’s totally thrilled, LOL. But if the Receiver is the issue, problems won’t be resolved by new sensors. How can Dex tech support figure out which component is malfunctioning?

Ancient thread, I know. Since this thread started and ended long before the Seven + came out, I am wondering if there's any new info on this particular subject?

In my case, I was on day 11 today, so I had restarted my sensor once already (last Friday afternoon). I got '???' for some time this AM, and then a few minutes ago I got 'SENSOR FAILED.' I didn't think to check in here first, so just pulled it off and put on a new one, but I'm now wondering if maybe I could have gotten it to restart even after having done a Start Sensor on the same sensor once already? Anyone know?

Thanks much,


Started a new sensor yesterday, and got Sensor Failed this morning. Have tried restarting it twice, and it goes into startup mode for a while, switches to "???" then finally gives "Sensor Failed". I've now done this three times. Am I beating a dead horse?

It would be nice to hear from someone in here who might be able to explain this for me.


I notice the following:

a) sensor failed, usually cannot restart, but stop and restart can confirm bad status. I have had not much success restarting and replace.

b) on the dreaded ??? display, I have been able to restart some sensors. Others I find that if I offset my fingerprick reading input by plus 10 points, sensor will run sometimes. My sense to save time and at same time try and recover sensor, I do following:

c) make sure your bg is stable on caveman machine and if so stop and retart sensor. If any hope ok; sensor will restart after 2 hours and may run. At least lost time is cut to 2 hours and if it does not start up after 2 hours, I replace it.

There seem to be no real good answers here and the lack of rational descriptive error codes and information make debugging sensor/system in any meaningful way virtually impossible. ( Users are too stupid and worse yet we would be signing our own death warrent with the lawyers by providing useful help out there.) At least that is my impression after 1 year 2 months 24/7 running. I may have missed something and if anybody out there has better data to share - please add.

Not to be cheaky, which dead horse are you beating? Dexcom or yourself?

For me that answer is usually both.

While the lack of helpful useful data my not have meant to have been cavilear, but for many of us driving nasty body situations, the lack of some explanatory help or guidance on operating seems short circuited by the tacit approval of the device as a trend following device and eliminates any responsibility at FDA or Dexcom. I may be wrong but cannot explain the black hole of useful user information on a complex device operating on a complex multi organ; multi-hormone human system. This is not a timex wrist watch.

As I and others note that when it works and one gets acllimated to the 2 hour start up and all the oddities and learns to "interpret" the data and weirdness as well as living with the idiosynchonies of the sensors and body chemistry interaction, yes by golly it can be very helpful and in some cases most critical indeed to diabetics.

Thank you for writing and sharing.