im having the same issues. i just replaced the rear pads and rotors. now 2 days later abs light starts going in and out. now its on constant. it rained yesterday while driving and it went out. only problem was it came back on after drying out... anyone have any ideas??? what / where could i check sensor?

2003 with 4wd suburban

 

Unless you check the codes on scanner its hard to say which side sensor has gone bad or connector corroded.
Or try to clean the debris from reluctor and sensor,see if this helps.