Steering: Description and Operation

The Variable Effort Steering (VES) System uses inputs from the Vehicle Speed Sensor and Steering Wheel Rotation Sensor to determine the desired amount of power steering assist. The power steering assist is controlled by the Power Steering Control Module.
The Power Steering Control Module constantly compares the amount of current actually flowing through the Power Steering Solenoid Actuator to the desired current it has calculated. The Power Steering Solenoid Actuator is an electromechanical current regulated device mounted to the power steering pump. The Power Steering Solenoid Actuator has a pintle that moves in and out of an orifice, regulating power steering fluid pressure. The Power Steering Control Module can change the amount of current flowing through the Power Steering Solenoid Actuator by varying the Output Duty Cycle. The current through the Power Steering Solenoid Actuator at 0 mph is approximately 230-250 mA, and with a 60 Hz signal on the VSS input of the Power Steering Control Module approximately 600-650 mA. If the Power Steering Solenoid Actuator is disconnected, the pintle will be pulled out of the orifice for maximum power steering assist.
The Power Steering Control Module has the ability to detect faults in the Steering Wheel Rotation Sensor, the Power Steering Solenoid Actuator or the circuitry to those components. Any fault detected will cause the power steering assist to remain at maximum with the pintle in its normally retracted position for all speeds. For example, a short to battery voltage on the high side (CKT 1295) of the Power Steering Solenoid Actuator will cause the Power Steering Control Module to open the low side (CKT 1294) and the pintle will not extend to decrease power steering assist.
When the system is operating normally, increasing vehicle speed will decrease power steering assist, allowing the driver to have improved road feel and directional stability. When sudden steering wheel turns are made, as in evasive maneuvers, it is detected by the Power Steering Control Module through the Steering Wheel Rotation Sensor. When detected, the Power Steering Control Module reduces current to the Power Steering Solenoid Actuator, allowing greater power steering assist.