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Erratic Speed Sensor Readings

I have a new style, magnetless speed sensor, and lately I've been getting some really erratic readings. Say I'm cruising along on a flat road at 18 mph. The speed on the Garmin will jump up to 21, then down to 17, then 19, settle on 18 for a little bit, and then jump around again. Sometimes it goes totally nuts, and jumps up to like 36. Once or twice, when I was at a dead stop, it showed I was going like 12 mph, until I started moving again. I don't think this happened when I first got the 520, though I can't be sure. Some days are worse than others. I've tried to unpair and repair the sensor, which might help sometimes, for a little while, though again I can't be sure. If I turn off the sensor and rely on GPS for speed, I get smooth, sensible readings. However, I ride in New York City, so GPS readings are often erratic, which is why I got the speed sensor in the first place. I use the Garmin on another bike with an old style speed sensor with magnet, and it doesn't seem to have the same problem.

At first i thought the sensor was wonky, and I called Garmin (after trying to replace the battery, etc.). The sensor was out of warrantee (I got it before I got the 520), but out of the goodness of their heart, Garmin sold me a new sensor for $20. However, when I installed the new sensor, I got the same erratic readings, so the problem apparently isn't the sensor.

Has anyone else seen this happen? I browsed the forum, but didn't see any similar complaints. Does anyone know the cause, or have a solution? I'd appreciate any insight or advice.

0 tigermountrider over 8 years ago

One thing that can cause that is the battery contact not being tight enough. Try putting a piece of paper or something behind the battery to make the contact tighter. The sticker that comes on new batteries works well.

0 WILFRIED84 over 8 years ago

Thanks for the tip. I finally got around to futzing with the sensor. I put a boot behind the battery (I used a couple of layers of scotch tape; the cap was hard to close). It didn't solve the problem. I still get erratic readings. Any other thoughts? I'm also interested to know if anyone else has seen this sort of behavior.

0 tigermountrider over 8 years ago

There is an issue that I forgot about. The sensor detects the earth's magnetic field and can be affect by a magnetized chain. If the sensor is on the rear wheel try it on the front. Other than that and the battery contact issue, I haven't seen any posts about problems with the sensor. I have 3 of them and they are all rock solid.

0 Wingrid3r over 8 years ago

Also have speed sensor issues.

New to cycling, new to the 520 but tech savvy.

When I start a ride by pressing the 520 start button, the stats show motion and distance (small) while not moving an inch. I am not even swaying the bike back and forth trying to mount/dismount- just still. I'm thinking about pulling the wheel sensor and looking at padding the battery as others have suggested.

It is installed on the front wheel.

0 tigermountrider over 8 years ago

If the sensor paired and connected? If you spin the wheel does speed show? If the 520 is not connected to the sensor GPS will be the source of speed. Due to position error the Edge can show some movement when still with GPS.

0 _ch_ over 8 years ago

I have exact same issues since i started using Edge 520 with magnetless sensors 1+ month ago. After reading the forum and read what people suggested, i tried cleaning the battery contacts, unpair and pair again, changed new batteries 3 times, tried putting on both front or rear hub, and making sure my chain is not magnetised. Still my speed is erratic. Sometimes it only happens at certain location when I ride loops, but today was the worst experience so far. Basically the speed goes from 25 - 45 - 0 -77 - 22 - 0 throughout my entire 40km ride (non looping). It reach the point where I'm so irritated because the Edge 520 will stop recording and start recording even though I'm on the move.

Can Garmin support please help me with this issue? My Edge 520 software version is 3.1 (latest version). I know there is version 6 available but Garmin Express say my software version is most updated (i guess due to region). I attached data of my riding today. Please offer me a solution for this. Greatly appreciated.

0 tigermountrider over 8 years ago

This is just a user forum. Call support in your region to see about getting a replacement sensor.

In the mean time turn off auto-pause. With it off the GPS data will be continously recorded and the Edge data can be corrected using GPS data. Or just remove the sensor until you can try a replacement.

If the problem only occurs when you are doing loops in certain locations its remotely possible that there is some kind of magnetic interference. But I doubt that is the issue for the ride you posted.

0 _ch_ over 8 years ago

Yeah most likely i will remove and use gps in the time being. The auto pause keep sounding when i was riding and it really irritates me. I saw garmin support staff replying to some threads so i'm hoping that they can help me out here.

0 TANWIN72 over 7 years ago

Erractic Speed Sensor Reading

Hi, I am also experiencing the exact same problem. I have changed the sensor and I have even changed the 520 unit but no help at all.

0 tigermountrider over 7 years ago

Can you post a FIT file from a problem ride?