There are 2 different kinds of steering systems used on the Probe, the standard power steering system and the electronic Variable Assist Power Steering (VAPS) system.
The standard power steering system consists of a rack and pinion steering gear, a belt driven pump, and the necessary interconnecting hydraulic lines.
The non-electronically controlled power rack and pinion steering gear has an integral valving and power assist system. The valve body is an integral part of the steering gear housing. The pressure line and return line from the pump attach at the valve body. A rotary valve directs high pressure hydraulic fluid through external oil lines to the correct side of the rack piston.
A spring loaded pressure pad assembly is used to keep the rack in constant contact with the pinion. Rubber boots at each end of the rack seal out dust, dirt and contaminants. The steering gear housing is mounted on bulkhead with a rubber bushing and mounting bracket at each end. The mounting brackets are attached to the bulkhead with three bolts at each bracket.
The Variable Assist Power Steering (VAPS) feature automatically adjusts power steering pressure. VAPS provides light steering effort during low speed and parking maneuvers and higher steering effort at higher speeds for improved road feel. The VAPS system consists of the VAPS control unit, steering angle sensor, vehicle speed sensor, solenoid valve, test connector, and inter-connecting wiring.
The Variable Assist Power Steering System is completely automatic, with no driver operated controls. The system continuously monitors steering wheel angle and vehicle speed to determine when to adjust steering system pressure. The system opens a solenoid valve to provide full power assist at vehicle speeds less than 6.2 mph or when the steering wheel is turned more than 45° to the right or left. The system reduces power assist under other conditions.
The VAPS Control Unit has a special feature which should be noted before performing any VAPS diagnostic procedures. A slide switch located on the VAPS Control Unit allows for 10 percent harder steering effort or a 10 percent lighter steering effort from normal production setting. Note the position of this switch before proceeding with diagnostics.