Steering System - Electronic: Operation

The system uses a modified rotary valve in the steering gear with 2 separate hydraulic circuits (primary and secondary). During low-speed operation, pressurized fluid from the steering pump is directed to the primary circuit by the actuator valve.

As vehicle speed increases, actuator valve gradually diverts fluid to secondary circuit. Since the secondary circuit diverts fluid back to the pump, steering effort is increased due to less pressure in the steering gear. The actuator valve is a pressure-balanced variable orifice valve, controlled by a stepper motor-driven linear spool. The VAPS module computes inputs from a Vehicle Speed Sensor (VSS) to determine the output signal that will adjust the opening of the actuator valve.

The VAPS module is programmed to perform a self-diagnostic check every 16 milliseconds. If a fault is detected, the VAPS module will deactivate its outputs, allowing normal power steering function. The VAPS module is also programmed to perform a service diagnostic check if activated by a service technician.