Electronic Variable Orifice (Evo) Actuator (Saturn) Buick Riviera VIII

The Electronic Variable Orifice (EVO) actuator is a linear solenoid mounted in power steering pump. PCM controls both power supply and ground path for the solenoid, using a Pulse Width Modulated (PWM) signal. During periods of low speed turns (as determined by VSS input), EVO actuator is commanded to open more, allowing pump to provide an increased fluid flow for increased steering assist. During high speed straight-line steering, EVO actuator is commanded to restrict flow of steering fluid to steering gear. Unused steering fluid is returned to reservoir by way of a by-pass.