Okay, really weird thing going on. Just to confirm, i have a 99 silverado z71. though air in the system was my problem...but i bleed the entire system out today with new fluid in place. also, i bought the truck wrecked, so this is first time driving now. anyway, the abs light comes on all over the board. start up it is off, then start moving it comes on, then stop it goes off. then it might come on and go off again in different mph ranges......

i am thinking it is a sensor somewhere...just not sure.... this be your guess too??

 

i would say sensor too. as long as it isnt affeecting the performance of the brakes.

 

you got 2 in the front at each wheel. its got nothing to do bleeding the brakes

 

Check the wire coming out of your hub... connection can sometimes get dirty, or the wire pinched or cut. Expensive fix.... gotta buy a whole new hub