The electronic variable orifice (EVO) system increases or decreases the amount of fluid leaving the power steering pump. This provides the driver with a comfortable balance of steering wheel feel and power assist.
At vehicle standstill or at 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 an improved road feel and a greater directional stability at highway speeds.
A sensor mounted on the steering column detects the steering wheel movements associated with defensive driving maneuvers. A control module uses this sensor input and the vehicle speed in order to adjust the amount of current to the solenoid.
The EVO system consists of the following components:
| • | The power steering (PS) solenoid actuator is located on the power steering pump discharged fitting. |
| • | The EVO/Passlock™ module is mounted on the instrument panel carrier, beneath the radio. |
| • | The steering handwheel speed sensor (HWSS) is located in the lower bearing of the steering column. |
| • | The vehicle speed sensor is located on the transmission output shaft or on selectable four wheel drive the transfer case output shaft. |
| • | The powertrain control module (PCM) is located in the engine compartment on the left inner wheel well panel (diesel engines only). |
| • | The vehicle control module (VCM) is located in the engine compartment on the left inner wheel well panel (gasoline engines only). |
