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Workaround for notorious GPS problem on Forerunner 45s

4148870
over 3 years ago

As are many other people around here, I am also afflicted with GPS sometimes taking forever to find a fix on my Forerunner 45s.
Digging a bit into the problem, I found the reason, and how to work-around the problem, which I would like to share here.

Root cause (as I understand it)

In order to get a fix on the current location, GPS not only requires to get a signal from satellites, but also needs some sort of information on trajectories of them. So without any prior knowledge, a GPS device needs to "listen" to satellite signals for a while (ca. 15 to 30 minutes?) to guess their trajectories. Manufacturers like Garmin now assist the devices by providing information about the trajectories via internet. This, however, has to be kept up-to-date constantly. With Garmin, this assist is called CPE, and it should be updated whenever a watch is synced with the app on a phone that is connected to the internet.
When my watch has a current CPE file installed, I get a GPS fix in less than a minute. When the CPE file is expired, the GPS fix takes more than 20 minutes.
According to Garmin, the CPE file should be updated, every time the watch is synced with the app on my phone. Only, this simply does not happen.

How to check CPE status

If you have GPS problems, you can easily check if this is also the underlying cause in your case.
1. Long-press middle button on left side  --> menu opens
2. Tap middle button on left side once --> Info
3. Tap upper button on right side once --> Device-ID etc.
4. Tap middle button on left side once --> CPE status
This either states "CPE up-to-date" (or similar, I have German language), or "CPE expired".

How to work around

CPE is instantly updated when I sync the watch via USB-cable to Garmin-Express on my PC. So before I go out for a run, I check CPE status on the watch, and if it is expired, boot up my PC, start Garmin Express and plug in the USB-cable to watch and PC. Annoying, but it works...

My request to Garmin

As this is obviously not the intendes behavior of the watch, please fix it! 5 minutes of research on the internet tell me that the exact same problem afflicts many more products of your portfolio, and also that it is not a new problem. Honestly, if GPS is that unreliable, I could also simply buy a Chinese knock-off...

  • 0 over 3 years ago

    Good summary, but there is nothing new in it. This behavior is well documented and well known. This is the case with EVERY modern GPS device from any vendor.

    So this is NOT a remedy, but this is the way it works. Garmin will never fix it, the CPE file is needed by the Sony GPS chip.

    CPE file can be updated without phone or computer connection as well. Leave the watch outside (good sky visibility) for about 10-15 minutes with GPS ON (e.g. start an activity with GPS), untouched. It is important that the watch does not move while communicating with the satellites. If you move it, the time needed will be more. After 10-15 minutes the CPE file will be updated. 

  • 0 over 3 years ago

    You are correct however, the CPE file should be updated by either Garmin Express of Garmin Connect sync process:

    Syncing your device either through the Garmin Connect App, Garmin Express, or when a compatible device connects to a previously configured Wi-Fi network will ensure that it has the latest available satellite location information.

    I believe that with the latest software version 3.90 the former option is just broken. I have had FR45 since 11/2019 and the watch has been working just fine. It is only when they pushed out the 3.90 firmware (early October 2020) the CPE sync process via Garmin Connect became flawed.

    Also, I do not have access to neither Windows nor Mac computer and I can't sync with Garmin Express.

  • 0 over 3 years ago in reply to PG

    @PG How is this supposed to work? You think the watch will recalculate the CPE file on its own? Without being in sync with the Garmin Connect App?

  • 0 over 3 years ago in reply to 6760491

    You are correct, I should have read the original post more carefully. CPE should be synced with phone app as well.

  • 0 over 3 years ago in reply to PG

    @PG I tried your trick today, left the watch on my balcony with a started activity for more than 2h. Nothing has changed, CPE still shows "Expired".

  • 0 over 3 years ago in reply to 6760491

    I am really surprised with this result. For me this always worked. The theory behind is that the watch receives all of the necessary information from the satellites, and about 10-15 minutes should be enough for that.

    Did you really start the activity, or just left it with GPS found? I ask this because if the recording was not started, the watch goes to battery saving mode after about 5 minutes, and switches the GPS off.

  • 0 over 3 years ago in reply to PG

    Yup, started an activity. Tried with both running and cycling. Nothing has changed with the CPE file status.

  • 0 over 3 years ago

    Why since last update (before I didn't have issues with GPS)...

  • 0 over 3 years ago
    4148870 said:
    Honestly, if GPS is that unreliable, I could also simply buy a Chinese knock-off...

    Good comment! My partner has had her A$320 45s for 3 days and it's been hopeless!  Her A$80 Huawei Band 3 Pro worked faultlessly and effortlessly for over a year before it died! NEVER had a problem locking onto GPS and did it at least as quickly as my Forerunner 35 does. The only thing stopping us from going back to the Huawei is lack of connectivity to other apps (eg: tracks can't be simply exported to Strava)

  • 0 over 3 years ago in reply to alanfw

    Yeah, you are right and Garmin support is far beyond what it should be! (they don't react at all)