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Steering System - Variable Effort Buick LeSabre VII

Electronic Steering 3 illustrations ~1280 words

DESCRIPTION & OPERATION

Variable Effort Steering (VES) system may also be referred 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. Decreased pump fluid pressure results in increased steering effort at greater road speed, providing firmer steering (road) feel.

The VES/TFE system consists of a Multi-Function Chime (MFC) module, Powertrain Control Module (PCM) and TFE actuator. TFE actuator is mounted to pump's 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 is accelerating and speed is between 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. If vehicle is still not moving after 3 minutes, MFC module de-energizes TFE actuator circuit to prevent overheating solenoid.
ComponentLocation
Fuse No. 5Near Right Kick Panel, In Relay Center
MFC ModuleBehind I/P, To Right Of Steering Column Support
PCMBehind Right I/P.l, Near Relay Center, Against Firewall
TFE ActuatorAt Pump Pressure Line Outlet

TFE SYSTEM ELECTRICAL COMPONENT LOCATIONS

Scheme 1

Scheme 1
Scheme 1

TROUBLE SHOOTING

Note. See the TROUBLE SHOOTING - BASIC PROCEDURES article in the GENERAL TROUBLE SHOOTING section.

SYSTEM CHECK

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

  1. Start engine and 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 «INCREASED STEERING EFFORT AT LOW SPEEDS»(/buick/lesabre/vii-1992-1999/remont/electronic-steering/#steering-system-variable-effort__increased-steering-effort-at-low-speeds) .
  2. Wait longer than 3 minutes with engine idling and vehicle not moving. Turn steering wheel to right and left. If wheel turns with greater effort than in step 1), system is okay. If wheel turns easily, see «STEERING EFFORT DOES NOT INCREASE AT SPEEDS GREATER THAN 20 MPH»(/buick/lesabre/vii-1992-1999/remont/electronic-steering/#steering-system-variable-effort__steering-effort-does-not-increase-at) .

INCREASED STEERING EFFORT AT LOW SPEEDS

Note. On Oldsmobile with optional gauge or digital instrument panel, TFE actuator is controlled by the instrument panel. On all other models, TFE actuator is controlled by MFC module.

  1. Turn ignition off. At steering pump, disconnect Two-Flow Electronic (TFE) actuator connector. Turn ignition switch to RUN position. Measure voltage between ground and Pink wire terminal of TFE actuator connector. If battery voltage does not exist, repair Pink wire circuit.
  2. If battery voltage exists, turn ignition off. Connect TFE actuator connector. Disconnect Multi-Function Chime (MFC) module connector (or Green and Orange 32-way instrument panel connectors on Eighty Eight with gauge or digital instrument panel). Turn ignition switch to RUN position. Measure voltage between Dark Green/White wire terminal of MFC module harness connector (or Orange 32-way connector on Eighty Eight) and Data Link Connector (DLC) terminal No. 5 (Black/White wire).
  3. If battery voltage exists, go to next step. If battery voltage does not exist, turn ignition off. Check for open Dark Green/White wire between MFC module (or Orange 32-way connector on Eighty Eight) and TFE actuator. If circuit is okay, replace TFE actuator. See «TFE ACTUATOR»(/buick/lesabre/vii-1992-1999/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 (or Orange 32-way connector on Eighty Eight) and Data Link Connector (DLC) terminal No. 5 (Black/White wire). Test drive vehicle at speeds less than 20 MPH (start engine and check steering effort on Eighty Eight, DO NOT test drive vehicle).
  5. If steering effort is easy at speeds less than 20 MPH, problem is in vehicle speed sensor, PCM, MFC module or related circuits. Repair as required. If steering effort is difficult, problem is mechanical. See «STEERING GEAR - POWER»(/buick/lesabre/vii-1992-1999/remont/manual-power-steering/#steering-gear-power) article.

STEERING EFFORT DOES NOT INCREASE AT SPEEDS GREATER THAN 20 MPH

  1. Turn ignition off. Disconnect Two-Flow Electronic (TFE) actuator connector. Measure voltage between Dark Green/White wire terminal of TFE actuator connector and Data Link Connector (DLC) terminal No. 16 (Orange wire). Measure voltage between Dark Green/White wire terminal of TFE actuator connector and DLC terminal No. 16 (Orange wire).
  2. If battery voltage exists, go to next step. If battery voltage does not exist, check TFE actuator connector for proper contact. If okay, problem is mechanical. See «STEERING GEAR - POWER»(/buick/lesabre/vii-1992-1999/remont/manual-power-steering/#steering-gear-power) article in this section.
  3. Disconnect Multi-Function Chime (MFC) module connector (or Orange 32-way instrument panel connector on Eighty Eight with gauge or digital instrument panel). Measure voltage between Dark Green/White wire terminal of TFE actuator connector (or Orange 32-way connector on Eighty Eight) and DLC terminal No. 16 (Orange wire). If battery voltage exists, repair short to ground in Dark Green/White wire.
  4. If battery voltage does not exist, check MFC module connector for proper contact. If okay, problem is in vehicle speed sensor, Powertrain Control Module (PCM), MFC module, or related circuits. Repair as required.

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 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 (SERPENTINE BELT)

  1. Serpentine belt tension is maintained by automatic tensioner. Ensure tensioner indicator mark on movable portion of tensioner is within limits of slotted area on stationary portion of tensioner. Any reading outside these limits indicates a worn belt or defective tensioner.
  2. If installing NEW belt, ensure tensioner indicator is within limit marks. If not, replace defective tensioner.
  3. If installing original belt, ensure belt's operating length and/or tensioner's operating range marks are not out of limits. Replace belt or tensioner as necessary.

RACK BEARING PRELOAD

  1. Raise and support vehicle. Turn front wheels to straight-ahead position. Loosen adjuster plug lock nut. (Scheme 2) Turn adjuster plug clockwise until it bottoms in housing. Back off adjuster plug 50-70 degrees (about one flat).
  2. While holding adjuster plug stationary, tighten adjuster plug lock nut to specification. See «TORQUE SPECIFICATIONS»(/buick/lesabre/vii-1992-1999/remont/electronic-steering/#steering-system-variable-effort__torque-specifications). Test drive vehicle, ensuring steering wheel returns to center after turning.

Scheme 2

Scheme 2
Scheme 2

TFE ACTUATOR

CAUTIONIf replacing power steering pump along with TFE actuator, ensure replacement pump is specified for TFE system. Non-TFE system pumps look identical, but are internally different.

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. Disconnect negative battery cable. 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 the «TORQUE SPECIFICATIONS»(/buick/lesabre/vii-1992-1999/remont/electronic-steering/#steering-system-variable-effort__torque-specifications) table below. Fill and bleed hydraulic system. See «HYDRAULIC SYSTEM BLEEDING»(/buick/lesabre/vii-1992-1999/remont/electronic-steering/#steering-system-variable-effort__hydraulic-system-bleeding) under LUBRICATION.

TORQUE SPECIFICATIONS

ApplicationFt. Lbs. (N.m)
Pump High Pressure Line-To-Discharge Fitting21 (28)
TFE Actuator46 (62)

TORQUE SPECIFICATIONS

Two-Flow Electronic Steering (TFE) System Schematic. Scheme 3

Scheme 3: Two-Flow Electronic Steering (TFE) System Schematic
Scheme 3: Two-Flow Electronic Steering (TFE) System Schematic