I got the new speed and cadence sensors this past week. My cadence sensor paired to my Fenix2 right away with no issues, but I appeared to have a DOA speed sensor. The speed sensor, on the other hand, was a beast. Tried the rear hub. Then tried it pointing the other way. Then tried the front hub. Took out the battery and put it back in, albeit quickly. I read a bunch on this site, as well as some of the other Amazon reviews, but it was only when I put together a number of the ideas that it finally "woke up".
(Side note: as others have said, make sure you don't use the combined 'Spd/Cad' setting on the Fenix2...you need to separately set up both the Bike Cadence and Bike Speed sensors separately.)
HERE'S WHAT EVENTUALLY WORKED FOR ME. YOUR MILEAGE MAY VARY:
-I removed the speed sensor from my front hub, took it out of the rubber housing, and took the battery out.
-I gently pried up the small gold battery contact, per another review.
-At this point, I placed it on a table about 20' from my bike (and the attached cadence sensor). I read elsewhere that the speed sensor should not be anywhere near another ANT+ sensor. Sounds dumb since they ship/work together, but whatever.
-I waited two minutes before putting the battery back in (something about shipping mode, who knows).
-Then I put everything back together: battery in, back in the rubber housing. Flipped the unit over in my hands twice and saw the green LED. Success!
I have no idea which of these little steps made it work, but combined they all worked. Would be nice if you didn't need to go through all of this, and the whole trial/error process cost me about a half hour. But it works now!
Good luck!
