1996 Ford Ranger ABS light Problem

I have a 1996 ford ranger it has 75000 miles on it 4spd 4 cly two wheel drive I got a problem with the abs light it come on and stays on for awhile then goes off I have taken it to a few places and had the codes check but they keep telling me that they cant find nothing wrong
can anyone give me a idea of what I should look for
Thanks