Join Date: Feb 2012
Thanked 58 Times in 47 Posts
Crank position sensor. I'd check to see if it's just come unplugged, but they're complete junk and if you fart too hard while riding it'll break the CPS.
I replaced my third or fourth one this weekend (losing count) after it cost me a DNF in a race. Of course I had a spare stator / CPS,, because eventually you figure out that you will always need one on hand.