When you turn the steering wheel in your car, the motion is transferred to the wheels so you can maneuver the vehicle. Power steering uses a hydraulic or electric system to make this easier so you don't have to exert very much effort to make a left turn. This system is most commonly paired with rack-and-pinion steering, which is the standard setup for most cars' steering systems.
Hydraulic power steering uses pressurized fluid flowing through a pump to power a steering gear. The system is very complicated, but essentially relies on varied pressure to facilitate movement of the wheels. When the steering wheel turns, the hydraulic pressure is applied to two pistons, one smaller than the other. This forces the pinion to slide in the appropriate direction on the rack, which moves the wheels. The hydraulic-only setup is becoming less common, as it is a relatively inefficient system. The need to maintain pressure takes away power from the rest of the engine, as the pump is connected to the drivebelt. This in turn leads to a decrease in fuel efficiency.
These days, most cars are equipped with either hydro-electric or electric power steering systems that are more efficient. The former setup still involves power steering fluid, which needs to be checked and changed regularly, while the latest advancement affords the system to run without the fluid, but we'll get back to that later. If your car has a hydraulic or a hybrid system, you will need to monitor the power steering fluid. Over time, the seals in the power steering system wear down and the degradation leads to particles in the fluid. At first, this will force the system to work hard, and the car will use more fuel. If ignored, dirty fluid can cause the hydraulic pump to break down.
To change the power steering fluid, you must first locate the reservoir and the pump. Use the owner's manual for guidance if you are unsure where they are located, as it varies between models. Remove the reservoir cap so pressure does not build up, and then disconnect the lower power steering pump hose. Drain all of the fluid into a drain pan, reinstall the hose and add new fluid. Fill the reservoir to the maximum fill line, replace the cap and you're done. Start the engine and turn the wheel all the way in each direction to get the fluid moving through the system. You may need to add a bit more fluid after doing this.
Since a fully electric system requires no power steering fluid, there is no need to worry about leaks or flushing the system. This is also the best setup to improve fuel efficiency. The hydraulic pump in other systems requires some of the engine's horsepower to run, which means it uses up fuel. Eliminating this need improves a car's fuel economy.
Rather than using pressurized liquid to make it easier to turn a car, the electric system relies on a motor mounted directly on the steering column. When the driver turns the steering wheel, a steering sensor relays the speed at which the wheel was turned and how far it moved. A torque sensor determines how much power is needed to adjust the column and these bits of information are transmitted to the power steering control module. The system also takes into account the car's speed and data from other onboard systems, such as the traction and stability control modules. This allows the electric motor to turn the column the precise distance for the turn the driver wants to make.