Principles of Operation

Special Tool(s)

Principles of Operation

NOTE: The Electronic Variable Orifice (EVO) steering system is not available on police vehicles.

The EVO steering system controls the level of power steering assistance based on vehicle speed and the rate of change in the steering position. Greater power assistance is provided at lower speeds to lessen steering effort and increase maneuverability. Less power assistance is provided at higher speeds to raise the steering effort for increased directional stability and greater "road feel."
Steering effort increases with vehicle speed in a smooth and continuous manner in the mid-range speed, reaching a constant level at high rates of speed. A high rate of change in the steering wheel position, which might indicate an evasive maneuver, will fit in an increase in the power assistance.
Vehicles with air suspension use the air suspension control module to monitor steering control for the Electronic Variable Orifice Steering (EVO) system. Vehicles with base suspension use the EVO control module to monitor the steering system. Both systems on a panic or aggressive turn will provide additional power assist. If there is any electrical system failure in the EVO system the system will default to full power assist.