My rear brake pad warning light came on yesterday, complete with the little "car on a lift" and gongs when starting the car. Very annoying! I tried resetting the light, and every time I would reset it, the display would show "-15000". I ordered a full set (front and rear) Hawk HPS pads online, then I checked the pads...DOH! They look brand new! I searched this forum, and after reading this thread, I called Napa and ordered a rear brake sensor cable, which was $26. They had it for me in a couple hours, so I picked it up on the way home from work. It took about 15 minutes to install. After installing it, I reset the rear brake pads in the dash, and it showed "31000" and the red light went out.
Long story short...I bought the car 8,000 miles ago, and someone must have replaced the pads and not the sensor. Now I have $155 worth of pads on the way that I don't need. I guess I will eventually need them.