Problems with brakes (ABS??)

When I use the brakes at a low speed (5-15mph), they have been "locking up" recently. It only does that at low speeds. I can slam on the brakes from 60mph and it will come to a stop properly. It seems that when I smash on the brakes, they work fine but using them normally (softer) causes the problem. When I say "locking up", the car jerks forward and the brakes basically do not work. I have to let off them and then try again which has led to a few close calls already. The ABS light has been off and on but not necessarily when they are messing up... Any advice would help

Have the ABS system scanned for codes. If the light comes on and off, there is a problem in the ABS system. A code can help isolate the area of concern. Otherwise, it is a guessing game and can be expensive.