Soft breaks throwing a DSTC Service error
 

I've had my 2000 S-80 for almost three years now, and the whole time I've owned it, it has had very soft / sensitive breaks that almost go to the floor before activating. In addition, almost everytime I drive the car the DSTC service come one, especially if I "ride" the breaks. I'm used to driving the car like this, but when anyone else drive it, it really freaks them out. Any ideas on what might be causing this, and how to fix it?