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This Paper describes a computer-controlled power steering system that has been developed and applied to production vehicles. The system provides full power assist at parking speeds, and gradually decreases assistance with increasing vehicle speed to give a normal unassisted “road feel” at highway speeds. The system enables a driver to choose one assistance characteristic among three choices at the flick of a switch, according to the driver's preference and road conditions. A solenoid-operated bypass valve is used to reduce the hydraulic fluid supply to the steering gear, which results in a heavier steering effort. The most suitable valve characteristic curve which corresponds to the increased pressure in the system due to the applied torque is discussed in this study. It is shown that detection of the velocity of steering wheel rotation and extension of the range of characteristics possible are effective ways to ensure good control over the power assistance.