1995 chev 1/2 ton abs light on on dash. Help.

On my 1995 chev 4x4 truck the abs light used to come on once in a while. When I would shut the key off and restart then the light would go away for a couple of weeks.Eventually it would come back on but go away after cycling the key.Then what started happening sometimes is I would go to stop at a stop sign and on dry pavement and the abs would activate and do the usual abs brake pulsate, but only sometimes.Now the abs light stays on continuous on the dash and abs doesn't work.When scanning the truck it finds no codes even though it should be a hard code.I scanned it with a snap on scanner specifically abs in the menu.Any thoughts would be appreciated.