Garmin has started pushing software 23.40 to Fenix 8 owners, and for once the changelog does not dance around the problem. Buried between two smaller bug fixes is a line that says exactly what happened to a group of owners over the last few weeks.
"Fixes optical heart rate sensor not working."
That is Garmin on its own forums, confirming the fault we wrote about on October 3, and shipping the actual repair.
What Went Wrong in the First Place
Version 23.39 arrived in late September as a real feature release. It added the "OK Garmin" voice wake phrase, suggested running workouts and indoor XC skiing. On a subset of watches it also killed the optical heart rate sensor.
The failure was not subtle. The green and red LEDs on the back of the watch stopped lighting up entirely. No wrist heart rate. No Pulse Ox. No overnight HRV. Because those readings feed the rest of the system, sleep tracking and Body Battery data disappeared too, which turned a flagship multisport watch into something a lot less useful.
Owners tried everything. A full power-off for more than 90 seconds revived some watches. Others needed a firmware reinstall or a rollback to the older 22.44 build, which brought back the previous sensor hub firmware. Factory resets worked for a few. None of it was dependable, and some watches came back only to fail again a few days later. Garmin support even told one owner their watch might need replacing if the reinstall did not take.
Now it looks like none of that was necessary.
What 23.40 Actually Changes
The official rollout post on the Garmin Forums, written by a Garmin staff account, lists four changes in 23.40 since 23.39:
- Fixes crash when enabling active heart rate broadcasting via Garmin Connect Mobile
- Fixes silent mode not muting notifications
- Fixes optical heart rate sensor not working
- Fixes other minor issues
That is a compact hotfix rather than a feature drop. If you were hoping 23.40 would bring new training tools or an interface refresh, it does not. Garmin is treating this as a repair job, which is the right call given what owners went through.
The heart rate line is the one that matters most. It also means the dead sensor was a software fault after all, not failing hardware, which is consistent with what the recovery workarounds suggested. If your Fenix 8 or Tactix 8 lost heart rate after 23.39, install 23.40 before you accept that the sensor is broken.
Which Watches Get It, and When
The rollout began on October 13 and Garmin says it is sitting at about 20 percent of eligible watches, with the percentage climbing over time. That staged approach is normal for Garmin, but it means the update may not arrive on your watch for a few days.
You do not have to wait. On the watch, open the main menu, go to Settings, then System, then Software Update, and choose Check for Updates.
Coverage is broader than the Fenix 8 line alone. The Fenix 8 AMOLED (Non-Pro) announcement is the one carrying the explicit sensor fix, and Garmin has published a matching 23.40 rollout for the Tactix 8 AMOLED. Garmin Rumors reports the same build also reaching the Fenix 8 Solar, the Enduro 3, the Fenix E, the Quatix 8 and the D2 Mach 2, which fits the way Garmin ships a shared software branch across its outdoor family.
We covered the same flaw when it first surfaced, including the device list and the recovery methods that owners were using, in our report on the 23.39 heart rate failure. That piece is worth a read if you want the full picture of the symptoms, but the short version is that the repair is here now.
Not Every Fix Lands Cleanly
There is already one early complaint attached to the new build. A thread on the Garmin Forums titled "23.40 problem" describes alert sounds going very quiet after the update, with one owner saying the volume dropped to a level that made notifications effectively inaudible. That is a single report so far and it may not generalize, but if your alerts sound different after installing 23.40, you are not imagining it, and a check of the sound and volume settings is worth the two minutes.
Garmin has also had a rough software stretch beyond heart rate. The company shipped 22.44 earlier this year to clean up display complaints, and we followed the brightness bug that left some Fenix 8 screens stuck at full tilt and draining battery in our coverage of that fault. Taken together, this has been a year where the Fenix 8 line's software, not its hardware, has been the thing owners complain about.
If Your Heart Rate Is Still Missing
Install 23.40 first. If the sensor stays dark after the update has finished and the watch has restarted, then the fault is likely hardware and it is time to open a case with Garmin, because the change log gives you a clear statement that the software side was addressed.
While you sort that out, a chest strap keeps your training data flowing without relying on the wrist sensor at all. A Garmin HRM chest strap pairs over ANT or Bluetooth and feeds the watch directly, so your load and recovery metrics stay intact even with the optical sensor out of action.
If you are in the market rather than troubleshooting, the Garmin Fenix 8 range now runs on a build where this particular problem is understood and closed out, which is a better place to buy into the platform than it was two weeks ago.
Bottom Line
Garmin shipped a substantial update, a slice of Fenix 8 and Tactix 8 owners lost wrist heart rate, and now a 20 percent rollout of 23.40 is putting it back. The changelog says the quiet part out loud, which is more than affected owners got from support at the time.
The rollout is slow, so check for the update manually instead of waiting for it to appear. If you have been living without heart rate, HRV and Body Battery for the last few weeks, this is the release that should give them back. And if it does not, you now have a document from Garmin saying the software was at fault, which makes the warranty conversation a lot easier.
For the wider picture of where Garmin's software releases have been landing this year, our Fenix 8 update tracker keeps the running list.
Sources: Garmin Forums official rollout posts for Fenix 8 AMOLED (Non-Pro) and Tactix 8 AMOLED system software 23.40 (October 13, 2026), including the published change log and staged rollout percentage; Garmin Rumors' report on the Fenix 8 series stable version 23.40 and the wider device list; Garmin News' write-up of the 23.40 release notes; Gadgets & Wearables' October 14, 2026 report on the heart rate fix and the earlier 23.39 failure; and our own October 3, 2026 coverage of the 23.39 sensor failure.
