if youve had discs/pads changed recently, check the plugs to sensors has not be disconnected and not refiited etc... this would be 1st port of call, if still the same possibly a abs sensor on 1 of the 4 hubs failed, now you can bridge these out to eliminate ( i wont go into detail as some know it all will prob come in and try and correct me and i cant be doing with an argument...), also get a wire bush and clean all the hubs near and around the sensor on each hub, if still pants then deffo a sensor out, abs pumps etc very very rarely fail so id rule that out...
hope this might help a bit?