Dexcom G5 ERR121

So, this is the SECOND time in the past two months that we’ve had the “ERR121” error and Dexcom doesn’t seem to know what’s causing it. Now we won’t get a new receiver until TUESDAY because their shipping department doesn’t work on weekends (which sucks, because as you all know, our son happens to be SICK atm.)

I wish they’d figure out this error!

The guy I talked too on the telephone said he was Type 1 himself and uses the same unit. He recommended, when we’re changing out the sensor to “stop sensor”, but do NOT “shutdown”…just leave it running. He said he hasn’t had the ERR121 error, and he also doesn’t shut down the machine, so he asked if we’d try that.

Does anyone have any other info on what could be causing this error? It gets irritating to receive a new receiver every month…

It’s never crossed my mind to shutdown my G5 ever. I keep a recharger by the bed so when I see my battery getting low, I plug it in. Seriously, sometimes it’s one small thing that drives a piece of technology crazy.

Did you search the forum for ERR 121? There are three results that are not you. Maybe they have an idea.

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I just did. It seems, to some extent at least, that may be the issue. Seems like the people on here that got that error shut down their receivers during sensor changes. Strange part of that the booklet that came with it says to do that.

There’s your problem right there. Who ever reads the booklet?


I’m now being sent my SIXTH G5 since December. The previous five all had the ERR121 message. To say I’m annoyed is an understatement. But to Dexcom’s credit, at least the wait time today was only 2 minutes. A few months ago I waited for 49 minutes (I timed it) until a human being picked up the phone. I asked to speak to a manager and was put on hold for another 5 minutes. So at least that issue seems to be better. The receiver … well not sure why they can’t fix this. Seems to happen if you shut the receiver off completely. And you will probably say “well just don’t shut it off”, but I have some periods without wearing it and it seems totally senseless to me to keep something turned on and using power if it’s just sitting in a drawer somewhere. Hoping for a better solution/provider/receiver …

It might be something as simple as turning on your receiver 24 hours before you’re going to use it if it’s been sitting unused for a while. These aren’t mp3 players. They’d be much cooler looking!

Unfortunately that won’t work because as soon as you turn the receiver on you get the error message and then it’s completely non-usable. I mean the error message cannot be cleared. The receiver is completely 100% not usable. You can’t even shut the unit off at that point. So turn it on at any time is the problem

I got this error a couple months ago and did some forum searching. Another possible cause was using a different charger than the one that comes with it. It could be a coincidence but the one and only time I got the ERR 121 message was right after using a different charger.

I can confirm this is a problem. I stopped my sensor and then shutdown my Dexcom receiver. Immediately upon powering up the receiver I got an ERR121. No way to get around the error. New Dexcom Receiver on its way from Dexcom.

Well, lesson learned…don’t “shutdown” receiver…like…EVER. :smiley:

Just happened to me this morning. It kept waking me up last night saying I was dangerously low when I wasn’t, so I got fed up and selected “shutdown” so I could get some sleep. This morning it was on again (???) and it was time to change my sensor so I selected stop sensor, and then I wanted to just enter my morning dose into it, but it was in the startup screen and never finished starting up. Holding the button then resulted in the ERR121 and the air raid siren. Of course on a weekend!

I have had the same observation: NEVER shutdown, only stop sensor. I was forced to replace 2 receivers due to ERR121 before I figured it out. It has now been over a year with the same Dexcom receiver.

I just lost my second receiver due to ERR121. When I called in my first receiver, the Dexcom representative told me that this is a known software bug. It did not dawn on me that the replacement receiver would still have the same bug. Silly me. I asked the Dexcom representative whether the bug was fixed now. He did not know. He recommended not to use shutdown.

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I know this is an older thread but I ran into this error code after shutting down the receiver. I was able to fix it by running the firmware update tool from the dexcom website. The update notes that it fixes error codes.

When I initially called Dexcom they said it was out of warranty and that I should by a new receiver. When I suggested a firmware update they said it was a hardware problem and it wouldn’t help. So that representative was dishonest.

I would say perhaps not “dishonest”. I have had the problem which was caused by a bug in the (old non-touchscreen) Dexcom Receiver which manifests during a receiver powerdown under certain circumstances.

I worked with Dexcom Technical Support and we tried many things to recover my receiver including an attempt at a firmware update. Nothing worked. The receiver happened to have 1 month left on the warranty so it was replaced at no charge. I got lucky.

This issue is well known to Dexcom Technical Support and IMHO is a motivating factor with the release of the new touchscreen receiver which does not suffer from this particular defect.

It would be my guess that Dexcom Technical Support has worked this issue with many people and in their experience have found that a firmware update is not helpful. If that was able to resolve the issue, I am 100% positive they would suggest it as it would have saved them a significant amount in terms of receivers replaced under warranty.

There was obviously something slightly different about your case that allowed the firmware update to work. Consider yourself lucky !!!

To avoid the same issue (which is still present in the firmware update you did), do NOT power off the receiver within 15 minutes of ending a session and preferably within 1 hour (to be on the safe side). Unless I am going to be totally not using the receiver and putting it on the shelf for long term storage then I never power it down.

It might have been fixed in the newer version of the firmware because it mentions it the notes.

The representative pushed hard to make a sale.