There is high internal leakage.

Refer to the appropriate procedure:

The steering gear valve spool is sticking or damaged.

Refer to the appropriate procedure:

Steering Gear Replacement .

The pump pressure is insufficient.

Refer to the appropriate procedure:

Power Steering Pump Replacement .

The fluid level is low.

Add fluid to the power steering system.

Refer to Checking and Adding Power Steering Fluid .