Pedal Falls Away
WARNING: This page is about a different car, the 2005 Jeep Liberty. However, it is still accessible from the selected car via links, so may be relevant.
A brake pedal that falls away under steady foot pressure is generally the result of a system leak. The leak point could be at a brake line, fitting, hose, or caliper. If leakage is severe, fluid will be evident at or around the leaking component.
Internal leakage (seal by-pass) in the master cylinder caused by worn or damaged piston cups, may also be the problem cause.
An internal leak in the ABS or junction block may also be the problem with no physical evidence.