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  1. #1
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    Garmin GSC 10 speed sensor issue

    Been having some issues with my Garmin GSC 10 speed sensor. I run it with an edge 800, and the speed sensor / cadence are only on my indoor training bike that I ride on the rollers, so it's never been outside. Have had it 7 months and just started having problems with it.

    A few days ago the speed sensor starting acting very strange. Did 45 min on the rollers and the speed sensor wasn't working; total ride distance was 7 ft. Heart rate and cadence seem to be working fine.

    So I changed the single battery on the GSC 10 and did another ride. Speed was now showing up, but was very sporadic; showing a lower than usual speed, sometimes seemed accurate, and then when I really starting hammering, getting up past 20mph the speed would jump from 20 to 10 to 0 to 20, etc.

    I've since checked and double checked the magnet position/alignment, recalibrate using the little button on the side of the sensor, and cleared the memory on my Garmin. Rode again since doing this and the speed sensor is still not working right: sporadic readings (sometimes showing 1/2 of what the speed should be), 0 mph for a few seconds when I really put the hammer down, and just seems low from what I am accustomed to seeing on it while riding the rollers.

    Any troubleshooting suggestions or tips? What else should I try? Thinking maybe the speed sensor went bad and I should just warranty it?

    Thanks!

  2. #2
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    My two GSC 10's (one on mountain bike, one on road bike) do the exact same thing. They worked fine for about the first month I had them, then just like you... it would show about half the real speed, then the real speed, then 0. My distances would get all sorts of messed up. I tried recalibrating my wheel sizes and putting in the wheel sizes from the chart, and still had messed up results. Finally I just pulled the wheel sensor magnets off. I do put the magnet back on when I ride my trainer, and strangely enough I get good results. But if I'm doing a real ride, it messes up. The cadence part of the sensor work fine on both of my bikes.

    Not exactly any help to you, but at least you know you're not alone! I'm thinking I might just have to warranty mine when I get around to it.

  3. #3
    sheep in FOX clothing
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    Mine was doing that and I assumed the battery was low, then the problem went away when I rotated the spoke magnet 90 degrees (sideways) on the spoke.

  4. #4
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    Contact Garmin support, they send replacements units almost without any questions. One of my colleagues also heals his GSC 10 using hair dryer but I don't know if water is an issue here...

  5. #5
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    As ghettocruiser said first thing to check is always a magnet - sensor positioning!

  6. #6
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    Hmm, maybe I'll just trying rotating the magnet a bit and see. Usually it just pisses me off enough I yank it off there, as I hate my rides being interrupted and I'm OCD about having semi-good data. None of my units have been exposed to any water, so I know that isn't coming into play.

  7. #7
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    Quote Originally Posted by sooshee View Post
    OCD about having semi-good data.
    Same here, bad powermeter reading can ruin my training.... We're toy addicted probably Anyway try to put You magnet exactly on GSC arm line(there is a mark on arm ) and max 2mm from it.My GSC tend to shift a bit during car transport no matter how good attached...

  8. #8
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    Quote Originally Posted by sooshee View Post
    None of my units have been exposed to any water, so I know that isn't coming into play.
    You sure about that? Usually riding the trainer indoors results in a lot of sweat drippage. Sweat is conductive (and corrosive) and screws up electronics if left to sit. Sure there's no salt crust on it (or ever was)?

  9. #9
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    Quote Originally Posted by NateHawk View Post
    You sure about that? Usually riding the trainer indoors results in a lot of sweat drippage.
    Seriously? How much sweat one has to produce to make left BB stay (where GCS 10 seats) wet? I can't imagine such scenario, but you newer know...

  10. #10
    sheep in FOX clothing
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    After 5 months of success with the magnet turned sideways, mine is now getting no readings from the wheel. I'm gonna hope it's a low battery (cadence is still fine), although I'll try moving the arm a bit closer first.

  11. #11
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    Quote Originally Posted by gps4sport.com View Post
    Seriously? How much sweat one has to produce to make left BB stay (where GCS 10 seats) wet? I can't imagine such scenario, but you newer know...
    maybe the OP has a sweaty butt crack. I don't judge.

  12. #12
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    Called Garmin and they are sending out a new GSC 10 unit, under warranty. Hopefully the new one will last a bit longer.

  13. #13
    sheep in FOX clothing
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    Changed the battery, which had one year and maybe 3500 km on it.

    The CR2032 battery voltage was at 2.95V instead of 3.35V when new, which didn't seem like much of a drop, but replacing the battery did indeed get the wheels sensor back working. It looked pretty well sealed and there was no indication that any water had gotten in.

    I still need to angle the spoke magnet oddly to get a signal.

  14. #14
    thecentralscrutinizer
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    Of the three GSC-10's that I run, only one has failed and Garmin replaced it. I have had issue from time-to-time and it is most often positioning of the sensor. Sometimes I accidentally hit it going on the bike rack or trainer, removing a wheel, etc.

    The faulty sensor had broken a connection in the arm and wouldn't transmit from the wheel sensor portion.
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