Steering System - Variable Effort Buick Park Avenue I

DESCRIPTION & OPERATION

These models use a Variable Effort Steering (VES) system referred to as Two-Flow Electronic (TFE) steering system and is based on vehicle speed only. TFE system controls amount of power steering pump fluid pressure applied to steering gear.

At speeds of about 20 MPH or less, TFE system allows full pump fluid pressure to steering gear, resulting in easier turning of the steering wheel. At speeds of about 20 MPH or more, TFE system decreases pump fluid pressure, resulting in increased steering effort at greater road speed to provide driver with a firmer steering (road) feel.

The VES/TFE system consists of a Multi-Function Chime (MFC) module, Powertrain Control Module (PCM) and TFE actuator mounted to pump high pressure fitting. PCM receives signal from Vehicle Speed Sensor (VSS). Based on VSS signal, PCM provides a ground for VSS circuit of MFC module. Pump pressure is increased when MFC module energizes TFE actuator under the following conditions

1. Vehicle speed is 0-20 MPH.
2. Vehicle is decelerating and speed is less than 20 MPH.
3. Vehicle is idling and not moving for 3 minutes or less. (After 3 minutes if vehicle still is not moving, MFC module de-energizes TFE actuator circuit to prevent overheating solenoid).

TFE 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 may cause pump damage.

1. Turn ignition off. Raise and support vehicle with front wheels off ground. Using steering wheel, 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 air and bring 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 POWER RACK & PINION article in STEERING section.

SYSTEM CHECK

Note. Ensure fuse No. 5 in relay center is good before continuing.

1. Start engine. Immediately turn steering wheel to right and left. DO NOT wait for more than 2 minutes before turning steering wheel, as test results will not be accurate. If wheel turns with minimal effort, go to next step. If wheel does not turn with minimal effort, go to «DIFFICULT STEERING AT SPEEDS LESS THAN 20 MPH»(/buick/park-avenue/i-1991-1996/remont/electronic-steering/#steering-system-variable-effort__difficult-steering-at-speeds-less-than) .
2. Wait longer than 3 minutes with engine still idling and vehicle not moving. Turn steering wheel to right and left. If wheel turns with greater effort than in previous step, system is okay. If wheel turns easily, go to «UNWANTED ASSIST AT SPEEDS GREATER THAN 20 MPH»(/buick/park-avenue/i-1991-1996/remont/electronic-steering/#steering-system-variable-effort__unwanted-assist-at-speeds-greater-than) .

DIFFICULT STEERING AT SPEEDS LESS THAN 20 MPH

1. Turn ignition off. At steering pump, disconnect TFE actuator connector. Turn ignition switch to RUN position. Measure voltage between ground and Pink/Black wire terminal of TFE actuator connector. If battery voltage does not exist, repair Pink/Black wire circuit.
2. If battery voltage exists, turn ignition off. Connect TFE actuator connector. Disconnect MFC module connector. Turn ignition switch to RUN position. Measure voltage between Dark Green/White wire terminal (Black wire on Bonneville SE) of MFC module harness connector and ALDL connector terminal "A" (Black/White wire terminal).
3. If battery voltage exists, go to next step. If battery voltage does not exist, turn ignition off. Check for open in Dark Green/White wire circuit between MFC module and TFE actuator. If circuit is okay, replace TFE actuator. See «TFE ACTUATOR»(/buick/park-avenue/i-1991-1996/remont/electronic-steering/#steering-system-variable-effort__tfe-actuator) under REMOVAL & INSTALLATION.
4. Connect a fused jumper wire between Dark Green/White wire terminal of MFC module and ALDL connector terminal "A" (Black/White wire terminal). Test drive vehicle at speeds of less than 20 MPH.
5. If steering effort is difficult, problem is mechanical. See «POWER RACK & PINION»(/buick/park-avenue/i-1991-1996/remont/manual-power-steering/#power-rack-pinion) article in STEERING. If steering effort is easy at speeds of less than 20 MPH, problem is in; vehicle speed sensor, PCM or related circuits. Repair as required.

UNWANTED ASSIST AT SPEEDS GREATER THAN 20 MPH

1. Turn ignition off. Disconnect MFC module connector. Measure resistance between Dark Green/White wire terminal (Black wire on Bonneville SE) of MFC module connector and ALDL connector terminal "A" (Black/White wire terminal).
2. If less than 5 ohms exists, repair short to ground in Dark Green/White wire (Black wire on Bonneville SE). If more than 5 ohms exists, test drive vehicle at speeds greater than 20 MPH with MFC module connector disconnected.
3. If steering effort increases, replace MFC module. If steering effort is easy, problem is mechanical. For more information, see «POWER RACK & PINION»(/buick/park-avenue/i-1991-1996/remont/manual-power-steering/#power-rack-pinion) article in STEERING section.

TFE ACTUATOR

Note. Depending on engine application, it may not be necessary to remove power steering pump to replace TFE actuator from pressure line fitting of pump.

Removal & Installation

1. Remove power steering pump drive belt. Disconnect TFE actuator connector. Disconnect pressure and return lines from pump. Remove pump mounting bolts. Remove pump. Remove TFE actuator and "O" rings from pump.
2. To install, reverse removal procedure using NEW lubricated "O" rings. Tighten TFE actuator to specification. See «TORQUE SPECIFICATIONS TABLE»(/buick/park-avenue/i-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/park-avenue/i-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
• POWER RACK & PINION
• DIFFICULT STEERING AT SPEEDS LESS THAN 20 MPH
• UNWANTED ASSIST AT SPEEDS GREATER THAN 20 MPH
• TFE ACTUATOR
• TORQUE SPECIFICATIONS TABLE
• HYDRAULIC SYSTEM BLEEDING