When u press brake pedal it goes straight to floor
Massive brake fluid leak, totally failed brake master cylinder, could be an ABS problem but never heard of it causing the pedal to go to the floor, I'm leaning toward a failed master cylinder.
Check brake fluid reservoir. If it's full then the master cylinder internal seals are shot, and it needs replacing. If one or both cylinder tanks are empty, fill it, and look for a major leak as someone is pumping the pedal. Check the lines, calipers, connectors at all four wheels. The master cylinder can also leak so check that area also.
Once you figure out where it's leaking, replace that seal or hose, refill the brake fluid reservoir, and make sure to bleed the brakes from each caliper, starting with the rear ones, then do the front. Make sure there's no air left in the system.
Looking for a Used Grand Prix in your area?
CarGurus has 1,889 nationwide Grand Prix listings starting at $3,000.
Search Pontiac Grand Prix Questions
Pontiac Grand Prix Experts