Power steering, either hydraulic or electric, helps the driver steer the car with less effort. The systems provide more assistance at lower speeds, when it’s harder to turn the wheel, and less assistance as the vehicle is moving, when the steering wheel is easier to move.
Hydraulic power steering systems use the engine’s power and a belt to power a pump that pushes power steering fluid through the system. That fluid enables movement of a hydraulic piston in the steering gear, which greatly reduces the effort needed to turn the steering wheel.
Electric power steering uses the vehicle’s computer and a small electric motor. When the driver turns the wheel, the computer signals the motor to help move the rack and pinion.
If you hear noises when you turn the steering wheel, squealing when you first start the car, or a groaning noise, your power steering pump may be on its way out the door.
You can drive without power steering, but it's not recommended.
Low Fluid: A low fluid level is the most common cause of power steering noises. The power steering fluid reservoir is small and many people don’t think to check it very often, so it won’t take much fluid loss to cause a problem.
Trapped Air:If air is able to enter the system, it can cause noise and unexpected vibrations when the steering wheel is turned.