Speed Sensor 2 - Software v4.0

They are weirdly silent on this. My Garmin is wanting me to update to 4.0 every single time I pair the sensor, but it can't download it anymore so it eventually fails. This is some bush league software management going on.

Try to put the sensor next to the Garmin, I updated mine this way for me yesterday.

I’ve tried many times. It counts up to about 65 and then says Connection Failed. The sensor alternates green and red for a while but then it seems to go to sleep. I’ve tried spinning it to keep awake but it doesn’t matter. I’ve probably tried to update it at least 10 times now. 

I don’t even want to update it. I just want it to stop asking me every single time I turn on the Garmin. 

I'm having the same issue as well. Following

I just updated my SPD to 4.0.  The first two attempts failed at 67 and 98.  The third time was the charm.

Then my Edge Explore said it was waiting for the speed sensor to restart.  There was also a popup with the caption "Update Successful" and a checkmark.  The restart counted increased to 67 and stalled there for over 5 minutes.

So I pressed the Update Successful checkmark and power cycled my Edge.  It booted fine, connected to the speed sensor when I spun the wheel and the Edge Explore started to display a speed value.  The SPD entry in the SENSOR setup screen showed V4.0

I'm thinking the first two update failures may be due to Bluetooth range limit (phone was in another room).  I suggest moving the phone next to your Edge device, make sure your Edge is properly paired to  your phone, and make sure your Edge is fully charged and your SPD sensor has a fresh battery.

These are the usual suspects, and since Garmin provides no information about update or the communications flow path. hopefully one of the above will solve your problem

I just took my sensor off the bike and made sure it was close to the head unit and phone and was the only sensor attached to the head unit. I also took it all away from the bike where none of the other sensors could connect during the update. It updated with no problem at all when it was away from all the other "noise". I had tried probably 20 times over the last few weeks with no success until I tried this option and this worked for me. I have a few of the same speed sensors on my other bikes. I'll give this a try with them as well and see if it works for them. I think it was trying to update from v2.3 to v4.0 just in case that info is useful. I'll report back if it's repeatable ;)

yeah, I had some issues, and after one or two times of unsuccessful update, I have turn of Bluetooth in  my mobile, and update went smoothly. But still not sure why it's not available (what I read from forum), what is reason of it.

I've had several failed upgrade attempts. The sensor fell asleep at 64 (1 attempt) and 99 (2 attempt) percent. In the first case, the sensor was on the wheel, and in the second it was lying next to the bike computer. I assumed that the sensor was just falling asleep, so during the third attempt I rotated the sensor a little. It was the third attempt that ended in success. I hope this helps someone.