Brake pedal rock hard ,grand voyager 2.8 diesel ,year is 2006

It is possible the problem is ABS related but could equally be a problem with the vacuum servo or brake booster or the "supply" of vacuum.

Certainly best practice would be to begin by ensuring the brakes at each wheel are in good order.

Test the brake servo by pressing the brake pedal vigorously several times while stationary with the engine off. The pedal should then feel higher than usual and rock-hard.
Apply the footbrake with a moderate force and start the engine without using the accelerator pedal, if possible. The brake pedal should be felt to pull itself down under your foot immediately the engine starts and stop pulling down in just two or three seconds, maybe just a second or two more if it is a diesel model.

Release the brake, allow the engine to idle for a few seconds longer and switch off. Listen carefully in the resulting silence for the sound of air leaking. This might have to be repeated several times in order to listen under the dash and in the engine compartment around the brake booster and vacuum lines. A short piece of garden hose used as a listening tube can be useful.

Once a servo has been charged with vacuum, in the absence of leaks, it should remain charged for a long time if the brake is not used - certainly hours but often months or even years is not unusual. Aplly a moderate pressure to the brake pedal and a shhhhh... sound should be heard that lasts about a second and then stops. Increase the pedal pressure and another shhhh sound and stop.

If all tests ok you can be reasonably confident the brake booster and vacuum lines are in order though it is still possible the vacuum supply is insufficient for sustained braking. A road test on a clear and safe downhill route will determine if this is so. Make a rapid series of brief brake applications at a constant speed of around 30mph and the braking effort and the feel of the pedal should remain consistent and if it does not it indicates restricted supply pipes or hoses, poor engine tune, incorrect idle speed (petrol models) or a worn or inefficient vacuum pump if it is a diesel.

Sounds like you have a dirty or bad Speed sensor (ABS). The griding is actually the ABS pump kicking in because it's getting false readings. Clean or replace the sensor(S) in the front wheel hubs. It is recommended to NOT drive the car until this is fixed. (WHY???) Because even though right now they seem to work, one of these times you will go to hit the brakes, they will become rock hard and you will bot be able to push on the pedal, you will have an accident and could be seriously injured.

with the head lights off ,and if you step on the brake pedal does the brake lights come on?

usually a stiff brake pedal is good, but if it is excessively stiff, it is usually caused by the brake booster

You likely have a defective power assist power brake booster, have a brake shop confirm this for you.

Your problem might be with the brake light switch. This switch is under the brake pedal, and when the pedal is pressed, it lets you shift your van out of park. This switch also activates the brake lights when you press the brake pedal. Try checking if your brake lights work. These switches are inexpensive, and very easy to replace.
Matt

I suggest check your brake light switch; generally, this is located in back side of ther brake pedal; also, confirm if your brake lights work fine.

Additional details could find in your additional questions: 96_plymouth_grand_voyager_stuck

Good luck.

It could be worn out brake pads or a small rock can sometimes get lodged into the brake mechanism. Try putting the car into reverse and tapping the brake repeatedly while the van moves. This will sometimes kick the rock out. Hope this helps!

master cylinder?

Replace the brake light switch on the brake pedal,this is the most common solution to your problem.