When you run the test by pressing the reset button, if you don't get a green LED for every pass of the wheel magnet for about sixty passes, then either your magnet isn't lined up or your GSC-10 is toast. The little o-ring Garmin put on the battery cover deforms very easily if over tightened and moisture gets in. I have an old GSC-10 that got water in it 10 years ago and the wheel sensor part quit working even though I tried to dry it out. Maybe I should try it again. I left the battery cover off of it, so now I just have to figure out where it is.