Description & Operation

The Variable Assist Power Steering (VAPS) control system consists of a control module, high-efficiency power steering pump, rack and pinion, actuator valve assembly and interconnecting hoses.

The VAPS system controls power steering fluid pressure through actuator valve assembly, mounted on rack and pinion. Actuator valve is a pressure-balanced variable orifice valve, controlled by a stepper motor-driven linear spool.

The system uses a modified rotary valve in steering rack with 2 separate hydraulic circuits. During parking and low-speed operation, flow from pump is routed through primary circuit by actuator valve. As vehicle speed increases, actuator valve gradually opens, diverting an increasing amount of fluid into the secondary circuit.

The VAPS module receives inputs from vehicle speed sensor and signals the stepper motor-driven spool to adjust the opening of the actuator valve. VAPS module is programmed to perform a self-diagnostic check every 16 milliseconds. If a malfunction is detected, control module deactivates its outputs. VAPS module is programmed to perform a service diagnostic procedure when activated by service technician.

The C-II pump is a 10-slipper pump with an integral reservoir. Spring-loaded slippers within cam and rotor create the pumping action. A flow control relief valve maintains pump volume and pressure.

The pump design incorporates a swiveled pressure fitting. 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.