A basic scanner won't track ABS. I believe a professional scanner can do this. You may have a faulty brake pressure switch, or faulty ABS module. a ABS capable scanner should tell you exactly what the part is throwing the light on. Not too fluent with ABS systems so that's about as far as I go here. good luck. may want to google/wiki what components make up a generic ABS system. I doubt it's your wheel speed sensors because you describe it only happening under harder braking. A wheel speed sensor would trip the light under all moving conditions regardless of braking intensity unless your driving on ice or something. anyway. good luck