Roadmaster Estate Wagon V8-350 5.7L VIN P SFI (1996)
Power Steering Pressure Control Valve: Description and Operation
The Variable Effort Steering (VES) System uses inputs from the Vehicle Speed Sensor (VSS) and the Steering Wheel Speed Sensor to determine the
desired amount of power steering assist. The power steering assist is controlled by the Power Steering Control Module (PSCM).
The PSCM constantly compares the amount of current actually flowing through the Power Steering Pump Actuator to the desired current it has
calculated. The Actuator is an electromechanical current regulated device mounted to the Power Steering Pump. The Actuator has a pintle that moves in
and out of an orifice, regulating power steering fluid pressure. The PSCM can change the amount of current flowing through the Actuator by varying the
Output Duty Cycle. The current through the Actuator at 0 mph in approximately 230-250 mA, and with a 60 Hz signal on the VSS input of the PSCM
approximately 600-650 mA. If the Actuator is disconnected, the pintle will be pulled out of the orifice for maximum power steering assist.
The PSCM has the ability to detect faults in the Steering Wheel Speed Sensor, the 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 1294) of the Actuator will cause the PSCM to open the low side (CKT 1295) 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, is detected by the PSCM through the Steering Wheel Speed
Sensor. When detected, the PSCM reduces current to the Actuator, allowing greater power steering assist.
