Usually e-brakes are not used very often and rust. Then when the do get used they don't return to proper position. Just take off your rear wheel and rotors and check it out. There are drum style emergency brakes on the inside of your rear rotors. My guess is some with some cleaning and lubing of the cables your emergency pads will return. Once you get them free and working you may want to use them more often to keep them working. Here is a vid that show the rear brakes 2002 Pontiac Grand Prix Brake Change - YouTube
