i have a 90 gmc suburban 4x4. the other day the brake light came on. now it is flashing a code. its like 1 long flash, a pause, then 12 quick flashes. it just down this over and over. the truck stops fine, it has no leaks, well at least none that i have found. there is plenty of fluid, and has new front brake pads. does anyone have an idea what this could be? the book i have on it doesn't say anything. thanks.