The vehicle's engine drives the power steering pump via a belt and pulley. The pump supplies the pressure necessary for the power steering rack or power steering gearbox to operate.  

Mechanics' Corner: More Technical Detail

Driven by the engine, the power steering pump pumps the power steering fluid (under very high pressure) to the steering rack. By means of the control valves within the steering rack assembly, the controlled flow of the high pressure fluid to an assist piston aides the driver's steering efforts. The assist piston continously mimics the driver's steering inputs, thus reducing the driver's effort while still allowing a natural feel. More modern versions—known as variable assist steering—are designed to provide less assist as the vehicle's speed increases, which provides a more natural sense of road feel.

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