Description & Operation
Variable Assist Power Steering (VAPS) control system automatically adjusts power steering fluid pressure to provide light steering effort during low speed driving and firm steering during high speed driving.
VAPS system consists of a control module, an actuator valve assembly, power steering pump, rack and pinion steering gear and hoses. See Fig 1 . VAPS system controls power steering fluid pressure through an actuator valve, mounted on steering gear. System uses a rotary valve in steering gear with 2 separate hydraulic circuits. Primary circuit provides greater power assist than secondary circuit. At low speed, fluid is routed through primary circuit by actuator valve. As speed increases, actuator valve gradually opens, diverting fluid to secondary circuit.
Steering gear and valve housing are combined into an aluminum die casting. Quick-connect fittings are used on pressure and return lines. Fittings are designed to swivel and should not be overtightened.
The VAPS module is programmed to perform self-diagnostic checks every 16 milliseconds. If a fault is detected, VAPS module will deactivate output, allowing normal power steering assist. VAPS module is also programmed to perform service diagnostic checks if activated by a service technician.
Two types of power steering pumps are used. The Ford C-II pump, used on most models, is a 10-slipper pump with an integral reservoir. Spring loaded slippers within cam and rotor create pumping action. Flow control relief valve maintains pump volume and pressure. Atsugi power steering pump, incorporating a fender apron mounted remote reservoir, is used on Taurus SHO models. This is a vane type pump. Manufacturers do not recommend service of the Atsugi pump. If service is required, replace pump as an assembly.
An identification tag attached to reservoir body indicates pump model. Use model code when ordering service parts, as some differences in internal components do exist.