O.T. GMC power steering question.

The Electronic Variable Orifice (EVO) system increases or decreases the amount of fluid leaving the power steering pump. This provides the driver with a comfort able balance of steering wheel feel and power assist.

At vehicle stand still or very low speeds, the system allows full hydraulic fluid flow for maximum power assist and reduced steering effort. As the vehicle gains speed, a variable orifice closes at the steering pump which reduces the pump fluid flow. This action provides a stiffer steering wheel response for improved road feel and greater directional stability at highway speeds.

A sensor mounted on the steering column, detects the rapid steering wheel movements associated with defensive driving maneuvers. A control module uses this sensor input and vehicle speed to adjust the amount of current to the fluid flow actuator.