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ANSWER by Visitor , July 19, 2010
The body control module (BCM) controls an electronic variable orifice (EVO) solenoid located in the power steering pumps output fluid orifice. On vehicles equipped with real time damping (RTD), this function is handled by the electronic suspension control (ESC) module. The solenoid consists of a pintle valve that moves in and out of the orifice, regulating power steering fluid flow.
The BCM/ESC module varies the amount of steering effort by commanding more or less current to the solenoid. At low speeds, no current is commanded and the pintle is fully retracted. This provides maximum fluid flow and maximum steering assist for easy turning and parking maneuvers. At higher speeds, more current is commanded to the solenoid and the pintle moves closer to the orifice. This decreases fluid flow to provide firmer steering (road feel) and directional stability.