Most steering systems use a rack and pinion. As the steering wheel is turned, the teeth on the pinion gear at the end of the steering shaft move the steering rack left or right. The steering linkages and tie rod ends then force the front wheels to change angle. A power steering pump pressurizes hydraulic fluid. When the steering wheel turns, a valve in the rack and pinion assembly opens, allowing pressurized fluid to help move the steering rack in the desired direction.