Dexcom G5 question about ? ? ? on receiver

A post was split to a new topic: Prolonging the life of a CGM session

2 posts were merged into an existing topic: Prolonging the life of a CGM session

@dave is this a G5 or G4? I am curious about how they manage to prevent a user from using their phone.

Times when I see “???”

  1. Pressure. If pressure is put on the sensor, it will wildly go low then back up. Usually when sleeping (laying on it). This screws up the predictive algorithm and it can’t give you a confident prediction.

  2. Water. Sometimes after a shower or bath, moisture can become trapped. You can carefully remove the transmitter, blot dry it, then put it back on. This sometimes works.

  3. Old sensor. Sounds like at 3 days, this is not the case for you.

  4. Bad sensors. I once received a bad batch of sensors. After a bit of trial and error, we suspect the package was overheated in delivery. No proof though.

  5. Bad transmitter. This is rare but could happen. As others say, try different sensors from different lots if you can. Dexcom is very good at replacing bad sensors. If none of them work, maybe it’s the transmitter.

  6. Stay hydrated. Since the whole point is that it is measuring off of the interstitial fluid, if you aren’t hydrated–it won’t read correctly.


If Dexcom wanted to prevent anybody from using the Dexcom App it would likely be trivial on the part of Dexcom as it requires a Dexcom server account. Whether they choose to block or not, Dexcom is certainly aware of who uses the Dexcom App and almost certainly would be obligated to provide this information to Medicare upon request.

On the other hand if somebody were to use xdrip or some other 3rd party software that does not hit the Dexcom servers then it would most likely be impossible for either Dexcom or Medicare to know about this. However these solutions are obviously not appropriate for everybody. As well, it is reported that Medicare requires people to agree not to use anything other than the Dexcom Receiver for the data collection so people may feel obligated to keep their agreement.


Lots of great info on the causes. Thank you so much, everyone. I thought the ??? had resolved itself after 15 minutes, because I started getting normal readings again (and accurate), but then later on, kapow, it reverted back to ???.

9 posts were merged into an existing topic: Dexcom transmitter: how do you remove and reseat it in the sensor bed?

Just to clarify – this trick works when the problem has to do with the contact prongs being wet or not making good contact – but there are other causes for the ??? error.

For us, the bulk of the ??? errors appear to be that the fiber is not in proper position anymore, in part because my son is very lean, and keeping it in the fat layer is not easy. So, the large majority of the time, cleaning the prongs doesn’t help for us.

5 posts were split to a new topic: Dexcom: what happens if you don’t calibrate?

I see this when I am dehydrated.


Dave, I split your post into two threads, here is the second: Dexcom transmitter: how do you remove and reseat it in the sensor bed?. Hope that’s OK!

This may sound weird but I’ve noticed the dreaded ??? when my iPhone attempts or completes another Bluetooth connection (like in my car).

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My session only lasts a week. How do you extend it past that time? I had a problem last week and they sent me a new receiver. Everything seemed ok until tonight. I then got the 3?. When I checked my bg , it had nothing for about 45 min. I decided to call Dexcom but before I was able to reach anyone, my bg was back so I hung up. This is my new receiver. Was planning on a large bolus of Novolog because of presumed heavy carb dinner, but took less unless my count was wrong, rather than risk another hypo. I’m type2.

You should simply be able to click the “Start Session” or “Sensor Warmup” or whatever the phrasing is to start the session.
If you want to restart the same sensor then physically you simply do nothing with the sensor itself. Just leave it alone and hit the start option on the receiver.

Also note that I would be surprised if the three question marks has anything do to with the Receiver. At least in my experience that has never been the case.


Good job on not over using. ALWAYS do a finger stick before injecting if you have inconsistent readings, or if you have symptoms that don’t match you cgm. I had the ??? and the dotless screen shortly getting a new meter. It hasn’t happened since then. If you keep receiving weird or incorrect info, call Dex com and wait to talk to someone. In the beginning of my Dex com use, I had many questions and screwed up with the insertion many times. This company has the greatest, most knowledgeable staff of any company I have ever called. That always have the answers and NEVER let me feel like the fool I think I am when I start the call. I’m a night person so often my calls are in the middle of the night and they are still calming.

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@NanaKP I sometimes get the ??? on my receiver because I was either lying on the sensor, the receiver and sensor are too far apart/opposite sides (front/back) of my body, or I had covered the transmitter with something metal like a phone or laptop. The ??? usually resolves itself in 30 min or less, but when it doesn’t I stop the sensor and restart it. That generally takes care of the problem. I personally average 40ish days with a sensor in my thigh, and 20ish days in my belly. I get better more consistent readings in my thigh than anywhere else on my body.

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Not weird. I saw the ??? recently (with G4) when my Bluetooth keyboard lost its connection, and I had to push the pairing keys to re-establish a connection. Clearly my receiver got some confusing signals.

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i Believe that Dexcom put some kind of validation on the new machines.

When i go into day 7, and want to re-use the same sensor, it always shows it.

if someone from Dexcom can reply to the comment it will be great.

the topic is the 3 questions. “???”

I always get this when i must (7days of use) change the sensor; but try and use the sensor for additional few days. No problem during my first 7 days.
Anyone else have the same problem?

@Marinus it happens to me too when the sensor times out on day 7. Stop sensor /start sensor, wait the 2 hours, calibrate and my Dexcom is usually happy again.

That’s what i do, somehow after day 7 i more frequently get ???, but normally before day 7 none.