How can you tell if you have a bad sensor or a bad transmitter?

Just activated a new sensor which I had “soaked” (inserted but not activated) for 24 hours. So far, after another 12 hours, the readings have been all over the place. Normally the readings are great after soaking that long. How can I determine if the problem is the new sensor or the transmitter? I have an Endo appointment on Wednesday (today is Monday) and don’t want to go there with readings that are unreliable and therefore would like to put in a new sensor or transmitter today if necessary.

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Call the dexcom helpline. They will trouble shoot it with you and if they determine the sensor (or transmitter) failed, they will send a new one for free.

What you describe sometimes happens with a new sensor. In the worst case, it has taken 3 days for a new sensor to settle in after I insert it, but usually it starts giving a smooth, correct-looking graph sometime 12 to 24 hours after insertion. Probably it is not a transmitter problem.

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Dexcom said only sign of transmitter failure if a “signal loss” message and it lasts more than 30 minutes. Said everything else is sensor failure. Talked to Dexcom tech support but they didn’t seem to understand (or weren’t allowed to comment) when I asked them questions like, “resistance id 1177, is that too high”?

Yeah, they have to stick to the script. You can read about the transmitter errors that others have had. The fact that the transmitter is still talking to the sensor would lead me to believe it is most likely a sensor failure.

Chris, thanks.

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@RCA221 First, this really sounds like a bad sensor. I know you use xDrip+, and the G6 battery stats are essentially worthless. G5 stats are pretty right on, but I don’t know why there is a difference.

Second, from all I’ve read, the soak can actually negatively effect accuracy with the G6. Best not to do it.

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Thanks doc how have you been? I currently use the g5 but thinking of changing to the G6. I’ll have to change a lot of things if I go to T-Slim and
the G6.

@RCA221 I’m doing fine, thanks.

In xDrip, if the resistance is over 1000 it is questionable, if over 1400 it is bad and will be red highlighted in system status. So, although 1177 is within normal range, it is still a bit high. But that shouldn’t make the readings be off or erratic.

If you try another sensor with the same results, then maybe your transmitter is failing.

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Doc, I am sure the sensor was off and am soaking a new one now before heading out tomorrow.

Can I ask a couple of questions?

Just curious, what range should a brand new transmitter have for Resistance and Voltage A and B when it is first inserted?

I have no idea how to update to a more recent version of Xdrip. I am using Stable version and not Beta or Alpha. But how do you update? And if you update do you have to go back and amend all your settings or are current settings saved when you upgrade? I think this is the latest but didn’t get it on Xdrip: Install the latest Xdrip+ build apk file:

Just curious what pump, type sensor and app do you use? Of course the app is Xdrip!

PS. I now am using Native on Xdrip. My many weeks of tests were inconclusive but did reveal certain things to me so it wasn’t a waste of time.

@RCA221 From JamOrHam:

Lower internal resistance means it can push more power and is generally better, that figure can be used to assess some battery health but more usefully the quality of any battery replacement. We mark >1400 resistance as bad, >1000 as questionable and <750 as great. voltage a < 300 is marked as bad, voltage b < 290 is marked as bad

Actually, I use the latest nightly version. Two ways to get it. First one, you have to enable engineering mode. Tap the medicine dropper icon. Then in the treatment applet, tap the microphone and say “Enable engineering mode”. The words “engineering mode enabled” will be displayed. Then go to settings>Update settings and choose the newly available “nightly”. Now you will automatically be on the nightly track. Or when you tap the 3 dot menu on the upper right of the home screen and choose “check for updates” you’ll get the latest nightly if available.

Second way is to go to

And download the first apk in the list. (do this on your phone).

You won’t lose any data or settings if you update or downgrade. Nothing you have entered will be changed or deleted.

I use MDI, never even tried a pump. Currently using G5, but I only have 2 sensors left then it’s back nto G6. (I like G5 better, but Dexcom is pushing me to G6 on Medicare).

The only caveat, the latest nightly may break the watch’s ability to act as a collector. Seems to have happened about 8-10 updates ago. Has to do with the Google Play version. JamOrHam is working on a flashing fix for this on the SSW 3.


Hi Doc,

Your (well probably not yours) description of resistance is so helpful for the curious like me. So thanks.

So if I “Stable” is checked can I still enable Engineering Mode and click nightly, and will it send me stable version nightly if the version changes? I have already done “check for updates.” So did that automatically update me without me knowing it?

I ought to just ask you questions as opposed to creating topics? What do you know about TSlim? :smile: Kidding.

I have tons of G5 sensors and can easily send you a few boxes. Believe it or not I got sent a double order once and they never caught that so I have extras that I will probably never use. Just let me know and we can exchange details.

Yes, you can enable engineering mode no matter what update track you’re on. And if you’re on the nightly track you’ll be offered the download of the nightly version. They’re called nightly, but there are only about 7-10/ month.

If you checked to be on the stable track, you’ll be offered the download automatically for the stable version. But that only comes once in a blue moon.

All I know about T Slim is that I really don’t want one :blush:. And thank you so much for the offer of G5 sensors. But that would only put off the inevitable, so I think I’ll just dive into the G6. There’s just more versatility with the G5.

I think I have been made aware of a new version a couple of times. I remember a blip coming on the screen and disappearing so I assumed I had to so something to get the update but I don’t know what and the blip disappeared.

Even in the engineering mode you indicate you will be offered the nightly version. If it is only offered automatically, not updated automatically, how do I in fact update the newer version? Thanks for clarifying that my setting would be saved

@RCA221 You will be offered the download on the screen xDrip+ notifies you with. Just click OK and it downloads.

And you’ll only be offered nightly updates if you choose that track in update settings. Whichever update track you choose.

@docslotnick - wait, can you say more about the “soak” (this is “presoak,” yes?) negatively affecting G6 accuracy? I have started to do this with G6 after having 12+ hours of false LOWs on the first 12 hours after warm up of a new G6 sensor (almost inevitably in the middle of the night!). The presoak seems to have eliminated the incorrect readings and my sensor jumps right in with aligned-to-meter readings. But wondering if there’s a better/different way of doing things. Thanks - Jessica (I do not use xDrip)

Hi @JessicaD I read this at

Pre-soaking of the G6 with factory calibration is likely to give variation in results. If you do pre-soak, then to get best results, you will probably need to calibrate the sensor.

I have also talked Dexcom Support about pre-soaking. Of course, with all things Dexcom, YDMV.

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