Yep, my 2017 935 does the same thing. I haven’t done anything with it as I don’t really care about elevation data anymore

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I've been having the same issue. I would do a simple 4 mile run in my neighborhood which is super flat and my Garmin would show a 600ft elevation gain. I called them and they told me the same thing...soak it in soapy water, send it back, etc. Didn't really want to send it back so I dealt with it, but it was frustrating.

One day I was on the Garmin Connect website looking at one of my activities. Near the picture of the watch there's something that says "elevations correction." On mine it said disabled. I enabled it and elevation was corrected. My 4 mile neighborhood run went from 600ft of elevation gain to 96ft. I can't figure out how to do it on the app and I have to do it for every activity. I'm sure there's a way to set it as a default; I just haven't figured it out (maybe someone else knows).

The one thing I can never get to work is the temperature. I can never get it to read and if it does it shows 72 degrees for the entire workout.

If you swim or shower with the watch, it will happen again.

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This is a known issue to Garmin. Their 8.0 software updated F*d up the watch somehow that can't even be fixed by downgrading the version, beginning mid-March. Garmin support will give you the "have been swimming with it, and do you soak it" routine, but it's their fault. Elevations come out randomly doubled or tripled. When my 920xt lost the barometer, everything read as 32,000 feet. And I cared, because that kind of causes my effort to look awesome, but makes my training numbers all wrong.

Anyway, they have just RMA'd both my 935 and my wife's 935. Look on the Garmin forums for "elevation and temperature data is screwed on 935".

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I'm closer to the feathered end of the spear than the point.

I don't think this is unique to the 935. There were lots of reports of issues with the 920, too.

I have a 920. So far I have not had the issues YOU describe (0, 1600, 0, etc). However, I do get skewed altitude readings when I go from inside to outside quickly. I can see the "right shape", but it loos slanted. Like my whole run was on a hill instead of an out and back. I can see where the "normal" peaks are still. However, I find that if I've been outside for a while then the altitude curve looks about like the "corrected" curve, and I usually don't bother with the correction. I don't remember having this problem last year (same watch), but it has been consistent since the outside temps have been in excess of indoor temps (aka summer).

I assume this has something to do with a temperature correction factor that either isn't working right, or that the 920 doesn't have. I never really looked into the inner workings of the 920 altitude.

This was a widely reported issue with the 920xt, which I've experienced also. Garmin was good about warranty replacement. My best guess was that it was caused by salt build-up from ocean swims, but it's possible it was chlorine from pool swims, or something else. I don't know whether it's technically feasible to design a barometric altimeter that wouldn't be susceptible to similar issues, though.

I get something similar with my 920, usually on morning runs. I have an out and back 5k that's a gradual 100' uphill to the turnaround, but often the 920 shows me as starting 200' higher than the actual elevation, going level or slightly downhill to the turnaround, and then about 200' downhill on the way back...

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"I'm thinking of a number between 1 and 10, and I don't know why!"

I'm on my third 935. First was a warranty replacement due to altitude meter / thermostat failing. Second was a crash replacement where I chatted with the support guy for a while. He said chlorine kills the protective membrane for the thermostat/barometric pressure sensor (altitude). He recommended rinsing the watch after every pool swim to let it last longer.

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I have the same problem with my Fenix 3 HR from 2016.

I had to return my 935 for the similar issue when the barometer failed in April. Garmin support was excellent and I had new watch in a few days. You can restart your 935 in debug/test mode and find various test screens as shown in the attachment:

I had my 920xt replaced under warranty for wonky altitude data after about a year of ownership. But I'm a duathlete - that watch was never in salt water and I never went swimming with it in a pool or otherwise. Still, wonky-ass and replaced.

Chiming in to report that I'm having the same issues with my 935. Garmin Support was no help either. Very frustrating.

My F5 has the same problem. It’s stuck at 26k feet. I pretty much Everest every run and ride now. But I don’t care about elevation except at races but I use my Edge520 for that.

I have three Garmin devises and not one of them is close to the other as far as elevation. Chalked up as poor Garmin software.

Both my wife's and mine are having the same 0 or gigantic elevation gain issue. Mine is RMA'd for a different issue at the moment. Might do the same for my wife's 935 later.

I was thinking of buying a 935/F5 so I could use the Garmin running power, glad I didn't.
Guess the 735 w/Stryd is a safer bet.

Has anyone tried to update the firmware to "beta v8.99" and see if it would resolve the issue?


Forerunner 935 software version 8.99 Beta
as of May 11, 2018

https://www8.garmin.com/...details.jsp?id=11751

Just to answer my own question. No, v8.99 beta firmware didn’t fix the problem. :-(

This is definitely not a new issue for Garmin. I have a Fenix3HR with the same issue and I know people with 910 and 920 that have the same issue. In the past I had great success with Garmin customer service but this time was very frustrating.
As of now before a run where I care about elevation i will manually calibrate the altimeter with GPS and 95% of the time it holds up for the length of the run (sometimes even a few more after). Based on history I would not expect this issue to go away any time soon.

I do a lot of pool swimming, mine is also wacked.

Update: Received a notification before my run this morning that the firmware had been updated to 8.1. After my run, saw the elevation gain was being recorded again. Seems like the update fixed the issue.

Having the same issue with my 935. Tried warm soapy bath and a hard reset. Ill try to update and see what happens. I have a race this weekend, super frustrating.

how do you hard reset?

Kind of a first world problem :) I'm in the same camp
and my 935 has had some screwy elevation stats. I just got a 520 for my bike. I assume their bike computers do a way better job than what they can put on a wrist. Plus there's no chlorine or other chemicals to mess that up. Accurate elevation data doesn't matter all that much to me on runs, I think it's more of a cycling stat. Anyways, I think Garmin's answer is to spend more money on their stuff!

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"The first virtue in a soldier is endurance of fatigue; courage is only the second virtue."
- Napoleon Bonaparte