I have a 1999 gmc serria. The brake module went out (making a continuous buzzing sound). I unplugged it for a year or so. Then I removed the module and sent it off for repair. When I put it back on the buzzing was gone but the abs and brake light stayed on. From time to time when I start the truck the lights will go out. They will stay off until I turn the truck off. When I start it up again they stay on. I know the sensors are on the front wheels. I have checked the wheel bearings they are good. Is there a way to check the sensors? Or are they just as well to be replaced?

https://www.gmforum.com/trouble-shoo...r-test-296556/

also check for loose connections and clean under the sensor, there is a tsb for those trucks if you live in the corrosion belt stuff gets under the sensor causing improper activation of the abs you could go through a stop light