Variable Effort Steering Description. Pontiac Grand Am 1998

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 1998 🢒 Grand Am 🢒 Steering 🢒 Variable Effort Steering 🢒 Variable Effort Steering Description

The variable effort steering (VES) system varies the driver effort that is required to steer as the vehicle speed changes. At low speeds, the system provides maximum power assist for easy turning and parking maneuvers. At higher speeds, steering effort is increased in order to provide the driver with firmer steering (road feel) and directional stability.

The VES system varies the driver effort by reducing the power steering fluid flow from the pump as vehicle speed increases. When the vehicle is stationary, the system provides maximum flow. As the vehicle speed increases, the fluid flow is decreased.

The VES system consists of the following power steering components:

•	The electronic brake control module (EBCM)

•	The electronic variable orifice (EVO) actuator

•	The steering wheel speed sensor

•	The power rack and pinion

•	The power steering pump

Electronic Brake Control Module (EBCM)

The VES steering system software is contained in the electronic brake control module (EBCM). The EBCM processes vehicle speed information from the ABS wheel speed sensors. The EBCM uses the steering wheel speed sensor in order to provide a control signal to the electronic variable orifice (EVO) actuator located on the power steering pump.


(1)	Discharge Fitting
(2)	O-Ring Seal (Small)
(3)	O-Ring Seal (Large)
(4)	Power Steering Pump Actuator
(5)	Power Steering Pump Actuator Connector Position Clip

Power Steering Pump Actuator

The power steering pump actuator assembly is located at the power steering pump discharge fitting. The power steering pump actuator assembly contains an electronic variable oriface (EVO) solenoid-operated pintle valve. Fluid leaving the pump passes through an orifice in the actuator tip. When the EVO solenoid is grounded by the EBCM, the solenoid moves the pintle into the orifice. The movement of the pintle into the orifice reduces the power steering fluid flow. As vehicle speed increases, the pintle blocks more of the orifice.

VES system components are similar to non-VES power steering components.


(1)	Lower Spring Retainer
(2)	Steering Wheel Speed Sensor
(3)	Lower Bearing Spring
(4)	Lower Bearing Seat
(5)	Adapter and Bearing Assembly
(6)	Steering Column Jacket Assembly

Steering Wheel Speeed Sensor

The steering wheel speed sensor sends a signal to the EBCM when abrupt or evasive steering maneuvers occur.

Power Rack and Pinion

The design of the VES power rack and pinion assembly is the same as for a non-VES system, except for differences in valve machining. Steering wheel movement is transferred to the pinion. The pinion moves the rack left or right through meshing pinion and rack teeth. The force is then transmitted through the tie rod ends and steering knuckles in order to steer the wheels.

The power rack and pinion steering system has a rotary control valve. The valve directs hydraulic fluid from the power steering pump to one side or the other side of the rack piston. The piston is attached to the rack, and uses hydraulic pressure in order to move the rack left or right. The rotary control valve regulates the degree of assist by responding to the driver's torque input.

If the hydraulic assist is not available, manual control is maintained. When manual control is maintained, more steering effort is required.

Power Steering Pump

The standard vane-type pump provides hydraulic pressure for the system. The pump incorporates a special discharge fitting in order to hold the power steering pump actuator.