Steering System - Variable Effort Pontiac Grand AM IV

DESCRIPTION & OPERATION

The Variable Effort Steering (VES) system, also referred to as an Electronic Orifice (EVO) steering system, varies the effort required to turn the steering wheel. VES system provides firmer steering (road) feel at higher vehicle speeds and improves directional stability. At low speeds and during parking VES system provides maximum assist.

As vehicle speed increases, VES decreases the amount of pump pressure applied to steering gear assembly to increase steering effort and improve steering feel by use of a Electronic Brake Control Module (EBCM).

The EBCM can detect a sudden turn (such as in an evasive maneuver) through input from steering wheel rotation sensor, Anti-Lock Brake System (ABS) wheel speed sensors and VES actuator.

VES system consists of an EBCM, VES actuator, steering wheel rotation sensor and ABS wheel speed sensors. EBCM receives inputs from steering wheel rotation sensor and wheel speed sensors. Based on inputs from these sensors, EBCM varies the current to the VES actuator.

If VES actuator is disconnected, 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 controlled by the EBCM, fluid by-passes pressure line outlet and is routed back into pump, decreasing fluid pressure to the steering gear.

If a system fault occurs, EBCM sets a code. Code can be retrieved to diagnose fault. See DIAGNOSIS & TESTING .

VES STEERING SYSTEM ELECTRICAL COMPONENT LOCATIONS

Scheme 1

TROUBLE SHOOTING - NON-ELECTRONIC

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

DIAGNOSIS & TESTING

Note. For more information, see the ANTI-LOCK BRAKE SYSTEM - ABS-VI article in the BRAKES section.

Note. Tech 1 scan tester, most current Mass Storage Cartridge (MSC) and High-Impedance Multimeter (J-39200), or equivalent, are required to test parts of ABS.

Before attempting any diagnostic procedures, road test vehicle to verify complaint. Perform pre-diagnostic visual inspection to detect obvious problems. See PRE-DIAGNOSTIC INSPECTION . Repair problems if necessary, and retest vehicle.

If no obvious problem is found, scan ABS for Diagnostic Trouble Codes (DTC). Attach Tech 1 scan tester to Data Link Connector (DLC), and follow Tech 1 scan tester instructions to retrieve DTCs. If DTCs are found, proceed to diagnostic flow charts. Refer to the DIAGNOSTIC CHARTS in this article.

If no DTC is displayed, test drive vehicle while using AUTOMATIC SNAPSHOT feature of Tech 1 scan tester. See SNAPSHOT. If failures cannot be reproduced, use ENHANCED DIAGNOSTIC feature to reveal ABS fault history. See ENHANCED DIAGNOSTICS .

PRE-DIAGNOSTIC INSPECTION

Check wheel speed sensors for correct mounting and alignment. Inspect wiring harness for correct routing. Ensure connectors have good contact and are not damaged. Check front wheel speed sensor air gap for correct measurement. See WHEEL SPEED SENSOR under ADJUSTMENTS.

USING TECH 1

Note. Tech 1 scan tester, most current Mass Storage Cartridge (MSC) and High-Impedance Multimeter (J-39200), or equivalent, are required to test parts of ABS.

Insert most current MSC into Tech 1 to perform ABS diagnostic procedures. Plug Tech 1 into Data Link Connector (DLC) before turning ignition on.

Selecting Model Year

Turn ignition switch to RUN position. Select appropriate model year using function keys.

Selecting Vehicle

After selecting model year, enter type of vehicle being tested. Press NO until "B" is flashing. Pressing EXIT will return Tech 1 to previous screen.

Selecting Test Mode

Following test modes are available for diagnosing ABS

* Mode F0 (Data List)

Mode displays actual reading sent to Electronic Brake Control Module (EBCM) by each wheel speed sensor. While vehicle is driven, wheel speed information can be observed to determine if readings are comparable to actual vehicle speed. Stoplight switch status can be observed by pressing brake pedal.

* Mode F1 (DTC HISTORY)

Mode displays trouble code history data. Data includes number of ignition cycles since trouble code occurred. Up to 5 fault codes are included in ABS history data.

* Mode F2 (Diagnostic Trouble Codes)

Mode displays ABS Diagnostic Trouble Codes (DTC) stored by EBCM. Tech 1 will display any DTCs and brief description of DTC displayed. If no DTCs are stored, Tech 1 will display NO ABS CODES.

* Mode F3 (ABS Snapshot)

Mode helps isolate intermittent problems by capturing data before and after fault occurred. By selecting MANUAL TRIGGER, Tech 1 will wait for ENTER to be pressed before storing speed sensor information. All stored information can be displayed and examined for conditions that may indicate problem.

* Mode F4 (ABS Test)

In this mode, Tech 1 performs hydraulic modulator assembly testing to help isolate problems during trouble shooting. Mode is also used for manual control of hydraulic modulator motors, which is used before brakes are bled.

ENHANCED DIAGNOSTICS

Enhanced diagnostics feature, found in DTC HISTORY function of Tech 1, is used to locate intermittent problems in ABS components. This feature will provide information regarding frequency of intermittent fault and detailed order of last 5 diagnostic trouble codes set. See Tech 1 scan tester instructions for more information.

Tech 1

Connect Tech 1 scan tester to Data Link Connector (DLC). Select F2 for Diagnostic Trouble Codes (DTCs). After DTCs have been viewed, Tech 1 will display CLEAR ABS DTCS message. Select YES key. Tech 1 will now display HISTORY DATA WILL BE LOST. CLEAR DTCS?. Select YES key to clear DTCs.

Ignition Cycle Default

If vehicle power is cycled 100 times without a particular fault reappearing, DTC will be erased from EBCM memory. Ignition cycle counter will be reset to zero.

DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION

DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION

SYMPTOM DIAGNOSIS

If no DTCs are stored, go to DIAGNOSTIC CHARTS .

INTERMITTENTS & POOR CONNECTIONS

Diagnostic charts can be used to identify problems, but fault must be present during testing in order to correctly locate problem. Diagnostic procedures can help determine cause of intermittent problems in ABS electrical components. Most intermittent problems are caused by faulty electrical connections or wiring.

When intermittent failure is encountered, check for Diagnostic Trouble Codes (DTC) stored in ABS module. If DTCs are found, inspect related components and circuitry for poor connections. If no DTCs are found, inspect suspect circuits as follows

1. Check for poor mating of connector halves, or terminals not fully seated in connector body (backed-out).
2. Check for improperly formed or damaged terminals. Carefully reform all connector terminals of problem circuit to increase contact tension.
3. Check for poor terminal-to-wire connection. This requires removing terminal and wire from connector body for inspection.

If inspection does not help locate intermittent problem, use ABS-VI self-diagnostic system to identify suspect circuit

1. Display and then clear ABS-VI DTCs in anti-lock brake controller.
2. Test drive vehicle, trying to duplicate conditions causing problem or complaint. Stop vehicle, and record any DTCs set.

Program ABS-VI SNAPSHOT feature to identify intermittent fault. Use ENHANCED DIAGNOSTIC feature to re-create conditions causing DTC to set. Determine how often and under what conditions fault occurs. Analyze ABS-VI SNAPSHOT data for unusual conditions.

DIAGNOSTIC CHARTS

Note. For diagnostic procedures not covered in this article, see ANTI-LOCK BRAKE SYSTEM - ABS-VI article in BRAKES.

DIAGNOSTIC SYSTEM CHECK

Diagnostic system check is an organized approach to identifying a problem created by an Anti-Lock Brake System (ABS) or Variable Effort Steering (VES) malfunction. This should be the starting point for any ABS or VES diagnosis because it directs technician to next logical step in diagnosing a complaint.

Serial data is transmitted through Electronic Brake Control Module (EBCM) terminal No. 2 (ABS without VES) or No. 1 (ABS with VES). Switched ignition voltage is supplied through EBCM terminal No. 14, battery voltage is supplied through EBCM terminal No. 15, and switched battery voltage is supplied through EBCM terminal "A". Ground is supplied through EBCM terminal "B". (Scheme 2)

Note. Test numbers refer to numbers on diagnostic chart on (Scheme 3).

1. Indicates if EBCM is transmitting data.
2. Checks for serial data line malfunction.
3. Checks for proper connection of Tech 1 to DLC.
4. Checks multifunction alarm module fuse for open.
5. Checks HTR/AC fuse for open.
6. Checks for high resistance in EBCM ground circuit.
7. Checks for current DTCs.
8. Checks for proper ABS warning light operation.
9. Checks for history DTCs.

Diagnostic Aids

Excessive resistance in power or ground circuits will not allow EBCM communication. If EBCM communication is not possible, ensure ABS ground connection is good and there is no excessive resistance in any power supply circuits. (Scheme 3)

1. 10) Checks for possible short to ground in battery voltage feed circuit.
2. 11) Checks for possible short to ground in EBCM.
3. 12) Ensures short to ground is not due to physical damage of circuit.

Scheme 2

Scheme 3

Note. Test numbers refer to numbers on diagnostic chart on (Scheme 4).

Excessive resistance in power or ground circuits will not allow EBCM communication. If EBCM communication is not possible, ensure ABS ground connection is good and there is no excessive resistance in any power supply circuits.

Scheme 4

Note. Test numbers refer to numbers on diagnostic chart on (Scheme 5).

1. 13) Checks for possible short to ground in switched ignition circuit.
2. 14) Isolates short to ground to either circuitry or EBCM.
3. 15) Ensures short to ground is not due to physical damage of circuitry.

Excessive resistance in power or ground circuits will not allow EBCM communication. If EBCM communication is not possible, ensure ABS ground connection is good and there is no excessive resistance in any power supply circuits.

Scheme 5

Note. Test numbers refer to numbers on diagnostic chart on (Scheme 6).

1. 16) Checks for proper battery voltage at EBCM.
2. 17) Checks for high resistance in battery voltage feed circuit.
3. 18) Checks for high resistance in switched ignition circuit.
4. 19) Ensures malfunction is not due to poor terminal contact.
5. 20) Checks for high resistance in switched ignition circuit between fuse block and EBCM.

Excessive resistance in power or ground circuits will not allow EBCM communication. If EBCM communication is not possible, ensure ABS ground connection is good and there is no excessive resistance in any power supply circuits.

Scheme 6

DTC 43 VES STEERING WHEEL SPEED SENSOR CIRCUIT MALFUNCTION

A 5-volt reference is supplied to steering wheel speed sensor through EBCM terminal No. 12, to sensor terminal "A". Steering wheel position input to EBCM is provided through steering wheel speed sensor terminal "B" to EBCM terminal No. 23. Steering wheel speed sensor ground is provided through EBCM terminal No. 16. (Scheme 7)

Note. Test numbers refer to numbers on diagnostic chart on (Scheme 8).

1. Checks steering wheel speed sensor input to EBCM.
2. Checks for short between steering wheel sensor input and ground circuits.
3. Checks for short between steering wheel sensor Viscous Converter Clutch (VCC) and ground circuits.
4. Checks for short to ground in steering wheel sensor input circuit.
5. Checks for short to ground in steering wheel sensor VCC circuit.
6. Checks for high resistance in steering wheel sensor VCC circuit.
7. Checks for high resistance in steering wheel sensor input circuit.
8. Checks for poor terminal contact.
9. Checks for proper voltage output of EBCM.
10. Ensures malfunction is not due to physical damage of steering wheel speed sensor circuits.

An intermittent malfunction is most likely caused by poor connection, rubbed-through wire insulation, or wire broken inside the insulation.

The frequency of malfunction can be checked using enhanced diagnostic function of Tech 1. See ENHANCED DIAGNOSTICS under DIAGNOSIS & TESTING.

Any circuitry suspected of causing intermittent malfunction should be thoroughly checked for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wiring connections, or physical damage to wiring harness.

Scheme 7

Scheme 8

A 5-volt reference is supplied to steering wheel speed sensor through EBCM terminal No. 12, to sensor terminal "A". Steering wheel position input to EBCM is provided through steering wheel speed sensor terminal "B", to EBCM terminal No. 23. Steering wheel speed sensor ground is provided through EBCM terminal No. 16.

Note. Test numbers refer to numbers on diagnostic chart on (Scheme 9).

1. 11) Checks for proper voltage with steering wheel speed sensor disconnected.
2. 12) Checks for high resistance in steering wheel sensor ground.
3. 13) Isolates high resistance to either EBCM or ground circuit.
4. 14) Ensures open ground is not due to short to battery.
5. 15) Ensures malfunction is not due to circuit damage or poor terminal contact.
6. 16) Checks for short to B+ in steering wheel sensor input circuit.
7. 17) Ensures malfunction was not due to physical damage of circuitry.

An intermittent malfunction is most likely caused by poor connection, rubbed-through wire insulation, or wire broken inside the insulation.

The frequency of malfunction can be checked using enhanced diagnostic function of Tech 1. See ENHANCED DIAGNOSTICS under DIAGNOSIS & TESTING.

Any circuitry suspected of causing intermittent malfunction, should be thoroughly checked for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wiring connections, or physical damage to wiring harness.

Scheme 9

A 5-volt reference is supplied to steering wheel speed sensor through EBCM terminal No. 12, to sensor terminal "A". Steering wheel position input to EBCM is provided through steering wheel speed sensor terminal "B", to EBCM terminal No. 23. Steering wheel speed sensor ground is provided through EBCM terminal No. 16.

Note. Test numbers refer to numbers on diagnostic chart on (Scheme 10).

1. 18) Checks for proper voltage with steering wheel speed sensor connected.
2. 19) Checks for proper voltage with steering wheel speed sensor disconnected.
3. 20) Checks for short to voltage in steering wheel sensor VCC circuit.
4. 21) Ensures malfunction is not due to physical damage of circuitry.
5. 22) Checks for short between steering wheel sensor VCC and input circuits.
6. 23) Checks for proper resistance of steering wheel speed sensor.
7. 24) Ensures malfunction is not due to physical damage of circuits.
8. 25) Checks for open resistor in steering wheel speed sensor.

An intermittent malfunction is most likely caused by poor connection, rubbed-through wire insulation, or wire broken inside the insulation.

The frequency of malfunction can be checked using enhanced diagnostic function of Tech 1. See ENHANCED DIAGNOSTICS under DIAGNOSIS & TESTING.

Any circuitry suspected of causing intermittent malfunction should be thoroughly checked for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wiring connections, or physical damage to wiring harness.

Scheme 10

DTC 73 VES ACTUATOR CIRCUIT OPEN OR SHORTED TO GROUND

Battery voltage is supplied to VES actuator terminal "A" when EBCM commands ABS enable relay ON. Ground for VES actuator is provided through EBCM terminal No. 11, to actuator terminal "B". The EBCM controls amount of current supplied to VES actuator based on input from wheel speed sensors and steering wheel speed sensor. (Scheme 11)

Note. Test numbers refer to numbers on diagnostic chart on (Scheme 12).

1. Checks for proper operation of VES actuator.
2. Checks for high resistance in VES actuator control circuit.
3. Checks for short to ground in VES actuator control circuit.
4. Checks for high resistance in VES actuator power feed circuit.
5. Checks for short to ground in VES actuator control circuit.
6. Checks for short to ground in VES actuator.
7. Checks for an open in VES actuator.
8. Ensures open or short to ground is not due to physical damage of circuitry.

An intermittent malfunction is most likely caused by poor connection, rubbed-through wire insulation, or wire broken inside the insulation.

The frequency of malfunction can be checked using enhanced diagnostic function of Tech 1. See ENHANCED DIAGNOSTICS .

Any circuitry suspected of causing intermittent malfunction should be thoroughly checked for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wiring connections, or physical damage to wiring harness.

Scheme 11

Scheme 12

DTC 74 VES ACTUATOR CIRCUIT SHORTED TO BATTERY OR SOLENOID

SHORTED

Battery voltage is supplied to VES actuator terminal "A" when EBCM commands ABS enable relay ON. Ground for VES actuator is provided through EBCM terminal No. 11, to actuator terminal "B". The EBCM controls amount of current supplied to VES actuator based on input from wheel speed sensors and steering wheel speed sensor. see scheme 13

Note. Test numbers refer to numbers on diagnostic chart on (Scheme 13).

1. Checks for short to voltage in VES actuator control circuit.
2. Checks for shorted actuator solenoid or shorted actuator circuits.
3. Ensures malfunction is not due to physical damage of VES actuator circuitry.
4. Isolates malfunction to actuator solenoid or its circuitry.

An intermittent malfunction is most likely caused by poor connection, rubbed-through wire insulation, or wire broken inside the insulation.

The frequency of malfunction can be checked using enhanced diagnostic function of Tech 1. See ENHANCED DIAGNOSTICS .

Any circuitry suspected of causing intermittent malfunction should be thoroughly checked for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wiring connections, or physical damage to wiring harness.

Scheme 13

Variable Effort Steering (VES) Schematic (Achieva & Grand Am). Scheme 14

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.

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 FULL 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, check fluid level. Add fluid as necessary to bring fluid level to FULL COLD mark. Return wheels to center position. Lower vehicle. Continue to run engine for 2 to 3 minutes to raise temperature of fluid and eliminate trapped air.
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. On the 2.3L, the power steering pump is driven directly off the end of the intake side camshaft.

3.1L

1. Power steering pump is driven by serpentine belt. Belt tension is maintained by automatic tensioner. Measure belt tension with belt tension gauge.
2. If tension is not as specified, check belt operating range indicated by marks on tensioner. See SERPENTINE BELT TENSION table below. If belt is not within operating range, replace belt. If belt is within operating range, replace tensioner.

SERPENTINE BELT TENSION (1)

RACK BEARING PRELOAD

1. Raise and support front of vehicle. Center steering wheel. Loosen adjusting plug lock nut. (Scheme 2) Turn adjusting plug clockwise until it bottoms in housing. Back off adjusting plug 35-45 degrees (50-70 degrees on Cavalier and Sunfire).
2. While holding adjusting plug stationary, tighten lock nut to 50 ft. lbs. (68 N.m). Test drive vehicle, ensuring steering wheel returns to center after turning.

WHEEL SPEED SENSOR

Note. Wheel speed sensor gaps are not adjustable.

Front

Front wheel speed sensors are mounted to steering knuckle. Gap between sensor and 48-tooth ring should be .02-.07" (0.5-1.8 mm). Replace sensor and/or ring if gap is incorrect.

Rear

Rear wheel speed sensor and ring are contained in dust cap of integral rear wheel bearing. If rear wheel speed sensor fails, replace wheel bearing/sensor as an assembly.

Removal & Installation

Turn ignition off. Remove EBCM connectors. Remove EBCM attaching screws. Remove EBCM from firewall. To install, reverse removal procedure. Ensure plastic grommets are in place. Tighten screws to 17 INCH lbs. (2 N.m).

1. Remove steering column from vehicle. See «STEERING COLUMN»(/pontiac/grand-am/iv-1992-1998/remont/steering-column/#steering-column) in this section.
2. Remove column jacket bushing from lower steering column. Steering wheel rotation sensor is part of column jacket bushing. To install, reverse removal procedure.

1. Disconnect negative battery cable. Remove pump drive belt. Disconnect VES actuator connector. Disconnect pressure and return lines from pump. Remove pump mounting bolts. Remove pump. Remove VES actuator and "O" rings from 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»(/pontiac/grand-am/iv-1992-1998/remont/electronic-steering/#steering-system-variable-effort__torque-specifications). Fill and bleed hydraulic system. See «HYDRAULIC SYSTEM BLEEDING»(/pontiac/grand-am/iv-1992-1998/remont/electronic-steering/#steering-system-variable-effort__hydraulic-system-bleeding) under LUBRICATION.

Note. Wheel speed sensor wiring harness is not repairable. Replace wiring harness as a unit if damaged.

Removal & Installation (Front)

1. Raise and support vehicle. Disconnect sensor connector. Remove sensor and bracket retaining bolt. Remove sensor.
2. To install sensor, reverse removal procedure. Ensure sensor is correctly aligned and flat against boss. Tighten sensor attaching bolts to 106 INCH lbs. (12 N.m).

Removal & Installation (Rear)

1. Rear sensor is integral with hub/bearing assembly. Sensor and hub/bearing assembly must be replaced as a unit.
2. Raise and support vehicle. Remove wheel. Remove drum assembly. Disconnect sensor connector. Remove hub/bearing retainer bolts. Rotate axle flange to align large hole with each bolt location. Support backing plate to avoid damaging brakeline. Remove wheel bearing and sensor assembly. To install, reverse removal procedure. Hold axle flange nuts, and tighten bolts to 44 ft. lbs. (60 N.m).

Scheme 15

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

See also:
• TROUBLE SHOOTING - BASIC PROCEDURES
• ANTI-LOCK BRAKE SYSTEM - ABS-VI
• STEERING COLUMN
• DIAGNOSIS & TESTING
• PRE-DIAGNOSTIC INSPECTION
• DIAGNOSTIC CHARTS
• ENHANCED DIAGNOSTICS
• WHEEL SPEED SENSOR
• TORQUE SPECIFICATIONS
• HYDRAULIC SYSTEM BLEEDING