Steering System - Variable Effort Buick Roadmaster VIII

DESCRIPTION & OPERATION

Variable Effort Steering (VES) system varies the effort required by the driver to turn the steering wheel, providing a firmer steering (road) feel and improved directional stability at higher vehicle speeds.

As vehicle speed increases, VES system decreases the amount of pump pressure applied to steering gear assembly to increase steering effort and improve steering feel. As a safety feature, the VES control module can detect when a sudden turn is made (such as in an evasive maneuver), by input from steering wheel rotation sensor. The control module then signals the VES actuator to allow increased pump pressure to the steering gear, thus decreasing steering effort.

VES system consists of a VES control module, VES actuator, steering wheel rotation sensor and Vehicle Speed Sensor (VSS). VES control module receives inputs from steering wheel rotation sensor and vehicle speed sensor (VSS). Based on inputs from these sensors, VES control module cycles VES actuator on and off.

When VES actuator is off (de-energized), full pump pressure is allowed to flow through pump's high pressure line outlet, increasing fluid pressure to the steering gear. (Scheme 1) When VES actuator is on (energized), fluid by-passes pressure line outlet and is routed back into pump, decreasing fluid pressure to the steering gear.

VES SYSTEM ELECTRICAL COMPONENT LOCATIONS

Scheme 1

TROUBLE SHOOTING

Refer to TROUBLE SHOOTING - BASIC PROCEDURES article in the GENERAL TROUBLE SHOOTING section.

HYDRAULIC SYSTEM BLEEDING

Note. If air was introduced into hydraulic system during servicing, bleed system. Aerated fluid, which appears Light Tan in color, results in poor steering performance and will cause pump damage. Replace aerated fluid.

1. Turn ignition off. Raise and support vehicle with front wheels off ground. Turn wheels fully to left. Add power steering fluid to COLD mark on dipstick. Turn wheels from side to side several times, but DO NOT touch steering stops. Add fluid as necessary to maintain level at FULL COLD mark.
2. Start engine. With engine idling, add fluid as necessary to bring level to FULL COLD mark. Return wheels to center position. Lower vehicle. Continue to run engine for 2-3 minutes to eliminate trapped air and raise fluid to operating temperature.
3. Road test vehicle. Check for leaks. Ensure fluid level is at FULL HOT mark when fluid is stabilized at operating temperature.

POWER STEERING PUMP BELT

Note. See appropriate adjustment procedures under POWER STEERING PUMP BELT under ADJUSTMENTS in STEERING SYSTEM - POWER article in the STEERING section.

Determining Duty Cycle

1. If speedometer and cruise control are inoperative and ECM Code 24 is set, repair Vehicle Speed Sensor (VSS) circuit or replace VSS as necessary. If speedometer and cruise control are okay and ECM Code 24 is not set, check for open in Dark Green wire between VES control module and circuit splice.
2. If circuit is okay, connect Signal Generator (J-38522) or Signal Generator/Instrument Panel Tester (J-33431-B) to VES control module connector. Set Signal Generator (J-38522) to 60 Hz or set Signal Generator/Instrument Panel Tester (J-33431-B) to 54 Hz.
3. Connect Tech 1 scan tester with ABS cartridge. Select VES DUTY CYCLE TEST. Turn ignition on. Observe reading on Tech 1 scan tester. Based on reading, proceed to appropriate test

Duty Cycle About 20-30 Percent

1. Turn ignition off. Disconnect VES control module connector. Disconnect steering wheel rotation sensor connector. Turn ignition on. Check for open, short to ground, short to battery or poor connection in Light Green, Red and Black wires between steering wheel rotation sensor and VES control module.
2. If circuits are okay, turn ignition off. Connect VES control module and steering wheel rotation sensor connectors. Turn ignition on. Disconnect signal generator. Check voltage between ground and Red wire terminal of VES control module connector.
3. If 4.5-5.0 volts is present, go to step 5). If 4.5-5.0 volts is not present, turn ignition off. Disconnect steering wheel rotation sensor connector. Check voltage between ground and Red wire terminal of VES control module connector.
4. If 4.5-5.0 volts is present, replace steering wheel rotation sensor. See «STEERING WHEEL ROTATION SENSOR»(/buick/roadmaster/viii-1991-1996/remont/electronic-steering/#steering-system-variable-effort) under REMOVAL & INSTALLATION. If 4.5-5.0 volts is not present, check for poor connection at Red wire connector terminal of VES control module. If connection is okay, replace VES control module.
5. Turn ignition off. Disconnect steering wheel rotation sensor connector. Measure resistance between Red and Black wire terminals of steering wheel rotation sensor connector (sensor side of harness). If resistance is not about 8000-11,500 ohms, replace steering wheel rotation sensor. See «STEERING WHEEL ROTATION SENSOR»(/buick/roadmaster/viii-1991-1996/remont/electronic-steering/#steering-system-variable-effort) under REMOVAL & INSTALLATION. If resistance is about 8000-11,500 ohms, connect steering wheel rotation sensor connector.
6. Start engine. Check voltage between ground and Light Green wire terminal of VES control module connector. While observing voltmeter, slowly rotate steering wheel at least 360 degrees.
7. Twice during steering wheel rotation, low voltage readings should be .45-.65 volt, and high voltage readings should be 4.0-4.4 volts. Both low and high voltage readings should occur 180 degrees apart. Voltage should increase and decrease smoothly, and should never decrease to less than 0.3 volt.
8. If voltages are as specified, go to next step. If voltages are not as specified, check for poor connection at steering wheel rotation sensor connector terminals, and at Light Green wire terminal and terminal C1 (Black wire) of VES control module connector. If connections are okay, replace steering wheel rotation sensor. See «STEERING WHEEL ROTATION SENSOR»(/buick/roadmaster/viii-1991-1996/remont/electronic-steering/#steering-system-variable-effort) under REMOVAL & INSTALLATION.
9. Check for poor connection at Light Green wire terminal of VES control module connector. If connection is okay, replace VES control module.

Duty Cycle About 57-67 Percent

1. Turn ignition off. Disconnect signal generator. Remove VES actuator. See «VARIABLE EFFORT STEERING (VES) ACTUATOR»(/buick/roadmaster/viii-1991-1996/remont/electronic-steering/#steering-system-variable-effort) under REMOVAL & INSTALLATION. Connect VES actuator connector. With signal generator still disconnected, set signal generator to 60 Hz.
2. While observing VES actuator pintle (look in to hole with flashlight), connect signal generator for 3 or 4 seconds, and then disconnect for 3 or 4 seconds. Do this 2 or 3 times. If pintle does not move in and out, replace VES actuator. If pintle moves in and out, system is operating as it should; however, an intermittent problem may exist.
3. To diagnose an intermittent problem, connect signal generator. Observe Tech 1 scan tester while rotating steering wheel from full left to full right 2 or 3 times. Also, wiggle harnesses to steering wheel rotation sensor and VES actuator. If Tech 1 scan tester displays anything other than 57-67 percent duty cycle, return to DETERMINING DUTY CYCLE at the beginning of these test procedures.

No Duty Cycle Present

1. Turn ignition off. Disconnect VES control module connector. Connect a test light between battery positive terminal and terminal D2 (Black wire) of VES control module connector. If test light does come on, repair open in Black wire between connector and ground.
2. If test light comes on, disconnect VES actuator connector. Check for open, short to ground or short to battery in White wire between VES control module and VES actuator.
3. If circuit is okay, check for: short to battery voltage or open circuit in Brown wire between: VES control module and VES actuator; VES control module and ALDL connector; VES control module and ALDL connector.
4. If all circuits are okay, check for poor connection at White wire terminal of VES control module connector. If connection is okay, replace VES control module.

PIN D ALWAYS LOW

1. Turn ignition off. Disconnect VES control module connector. Connect a test light between ground and terminal C2 (Brown wire) of VES control module connector. Turn ignition on. If test light comes on, go to step 3). If test light does come on, check 20-amp fuse No. 6 in passenger compartment fuse block.
2. If fuse is okay, repair Brown wire between fuse and VES control module. If fuse is blown, replace fuse. If fuse blows again, repair short to ground in Brown wire between fuse block and VES control module.
3. Disconnect VES actuator connector. Check for short to ground in Brown wire; between VES control module and VES actuator, and between VES control module and ALDL connector. Also check for poor connection at terminal B2 (Brown wire) of VES control module connector. If circuits are okay, replace VES control module.

Note. Use the following test procedure if PIN D ALWAYS LOW is displayed for about 3 seconds, and then duty cycle changes rapidly from 25-80 percent.

PIN D ALWAYS LOW, Then Duty Cycle Changes

Check for open in Brown wire between VES control module and VES actuator between VES control module and ALDL connector. Also check for poor connection at Brown wire terminal of VES control module connector. If all circuits are okay, replace VES control module.

DECREASED ASSIST AT ALL TIMES

1. Disconnect VES actuator. If symptom is still present, problem is mechanical. Check power steering system. Proceed to «STEERING SYSTEM - POWER»(/buick/roadmaster/viii-1991-1996/remont/manual-power-steering/#power-recirculating-ball) article in the STEERING.
2. If symptom is no longer present, check speedometer and cruise control. If speedometer and cruise control operate properly, replace VES control module. If speedometer and cruise control do not operate properly, repair Vehicle Speed Sensor (VSS) circuit or replace related components as necessary.

Removal & Installation

1. In engine compartment, remove coupling bolt retaining intermediate steering shaft to lower end of steering column. Slide coupling off lower end of steering column shaft. Remove retaining clip and remove steering wheel rotation sensor from lower steering column.
2. To install, reverse removal procedure. Tighten intermediate steering shaft coupling bolt/nut to 40 ft. lbs. (54 N.m).

1. Remove pump drive belt. Disconnect VES actuator connector. Disconnect pressure and return lines from pump. Remove pump mounting bolts. Remove pump to access and remove VES actuator from rear of pump. (Scheme 1)
2. To install, reverse removal procedure using NEW lubricated "O" rings. Tighten VES actuator, and pressure and return lines to specification. See «TORQUE SPECIFICATIONS TABLE»(/buick/roadmaster/viii-1991-1996/remont/electronic-steering/#steering-system-variable-effort) at the end of this article. Fill and bleed hydraulic system. See «HYDRAULIC SYSTEM BLEEDING»(/buick/roadmaster/viii-1991-1996/remont/electronic-steering/#steering-system-variable-effort__hydraulic-system-bleeding) under LUBRICATION.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

Variable Effort Steering (VES) System Wiring Diagram. Scheme 2

See also:
• TROUBLE SHOOTING - BASIC PROCEDURES
• STEERING SYSTEM - POWER
• STEERING WHEEL ROTATION SENSOR
• HYDRAULIC SYSTEM BLEEDING