The amount of fluid that leaves the power steering pump is increased and decreased by the electronic variable orifice (EVO) system. Increasing and decreasing the amount of fluid leaving the power steering pump provides the driver with a comfortable balance of steering wheel feel and power assist.
The system allows full hydraulic fluid flow at vehicle stand still or at very low speeds. This allows 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 provides a stiffer steering wheel response for improved road feel and greater directional stability at highway speeds.
The steering wheel movements associated with defensive driving maneuvers is detected by a sensor mounted on the steering column. A control module uses this sensor input and vehicle speed in order to adjust the amount of current to the solenoid.
The EVO system consists of the following components:
| • | The steering assist control solenoid is located on the power steering pump discharge fitting. |
| • | The EVO/Passlock module is mounted on the instrument panel carrier, to the right of the steering column. |
| • | The steering handwheel speed sensor is located in the lower bearing of the steering column. |
| • | For diesel engines only, the vehicle speed sensor buffer is located on the bottom of the powertrain control module (PCM) tray. |
| • | For gas engines only, the vehicle control module (VCM) is located in the engine compartment on the left inner wheel well panel. |
