Im not sure what year it began but some are built into the hub and some arent. If it isnt its an easy fix I had the same problem! Water will get behind the sensor and in the hole causing rust to either pull it away or swell up the hole causing damage to it. Take of the brake caliper and remove the sensor. Plug the hole in the hub and remove all the rust that built up behind the sensor. Then if the hole swelled(you will know because the sensor will come out damaged)clean it out using a magnet to get it all out. Dont let anything fall into the hub. Clean the sensor off and apply hightemp grease all around the hole and the sensor keeping the tip clean. Put it all back together and it will be gone. If the sensor looks deformed or twisted in any way buy a new one. GM also had a recall on this!!!!!!!

 

Clean the ABS sensor, take to dealer also....... recall issue on the sensor. I have a 2002 and it kept doing that to me, finally a few months later was pulling in my driveway, it happened and rear ended my fiancee's car. Long story short GM paid the $2600 to fix both cars and replaced my sensor. But I still need to clean them about every two years.

 

My 2005 Silverado was doing this. I took it to a garage and they "fixed" the problem, $500 for one side. Said it was the ABS sensor. Now it is doing it again. I'm guessing the other side is bad. I am wondering if you can just pull the ABS fuse out and not have ABS. ? (I do not have the $500 right now to fix.) Anyone know?