When ABS operation occurs, the driver of the vehicle should always continue to push hard on the brake pedal. Never pump the brakes. The ABS system will automatically modulate the brakes
Pressure Hold
Isolation will occur when the driver applies excessive braking for the given road conditions, causing the wheels to decelerate at a rate which exceeds the vehicle's capability.

If the information from the wheel speed sensors indicate excessive wheel deceleration (imminent lock-up), the first step in the antilock sequence is to isolate the brake pressure being applied by the driver.

The EBCM applies a voltage to the isolation coil in order to close the isolation valve (3, 5, 13). This will prevent any additional brake pressure applied by the driver from reaching the wheel. With the isolation valve (3, 5, 13) closed, further increases in brake pressure from the driver will be prohibited.

Pressure Decrease
Once the pressure is isolated, it must be reduced in order to get the wheels rolling once again. Reducing pressure is accomplished by dumping a portion of the brake fluid pressure into a low pressure accumulator (LPA) (8, 11).

The EBCM energizes the dump valve coil(s) in order to open the dump valve (6, 9, 12), allowing fluid from the wheels to be dumped into the LPA (8, 11). Very short activation pulses open and close the dump valve passageway in order to control this action. Brake pressure is lowered at the wheel and allows the affected wheel to begin rolling again.

The fluid taken from the wheels forces a spring back. The fluid is stored in the LPA (8, 11) at approximately 1034 kPa (150 psi). A portion of the fluid also primes the pump (4, 15) so it can begin building reapply pressure. The dump valves (6, 9, 12) are opened independently in order to control the deceleration of the wheel.

Pressure Increase
The reapply sequence is initiated in order to obtain optimum braking at each wheel. The isolation valve (3, 5, 13) is momentarily pulsed open in order to allow the master cylinder (2) and pump (4, 15) pressure to reach the brakes (7,10). This controlled pressure rise continues until the wheel is at optimum brake output or until the brake pressure is brought up to the master cylinder output pressure.

If more pressure is required, more fluid is drawn from the master cylinder (2) and applied to the brakes (7, 10). The driver will feel pedal pulsations or pedal drop. This is normal and expected when in the antilock mode.

As fluid is reapplied, the wheels begin to slow down at the optimum rate. If the wheels approach imminent lock-up again, the module will isolate, dump and reapply. These control cycles (isolation, dump and reapply) occur in millisecond intervals, allowing several cycles to occur each second.
So basically, you will feel the pressure on the brake pedal pressure changing and hear the Brake Pressure Modulator Valve activating and deactivating.
Sorry about the long write up.