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Four Wheel Drive Systems: Other Ford Explorer III

Transfer Case 33 illustrations ~998 words

FOUR-WHEEL DRIVE SYSTEMS - ALL-WHEEL DRIVE (AWD)

The AWD transfer case is a two-piece aluminum, chain-driven, viscous clutch-type unit. In this system, AWD is always activated. This AWD is automatic and has no external controls.

FOUR-WHEEL DRIVE SYSTEMS - ELECTRONIC SHIFT

The automatic four-wheel drive (A4WD) system is an electronic shift 4x4 system that utilizes the following components

  1. transfer case
  2. four-wheel drive (4WD) control module
  3. mode select switch (MSS)
  4. gearmotor encoder assembly (part of the electric shift motor)
  5. electric shift motor
  6. shift motor sense plate (part of the gearmotor encoder assembly)

Electric Shift Motor

The externally mounted transfer case shift motor, located at the rear of the transfer case, turns the shift cam assembly. As the shift cam assembly turns, it positions the reduction shift fork for desired transfer case operation. An integral position sensor in the shift motor provides shift motor position information to the 4WD control module.

Mode Select Switch (MSS)

The push button MSS. mounted on the instrument panel, allows the operator to select the 4x4 Auto, 4x4 High, and 4x4 Low transfer case operating modes. The indicator light, on the instrument cluster push button, will illuminate only when the 4x4 Low position is engaged.

Brake Pedal Position (BPP) Switch

The BPP switch is located on the brake pedal. The switch signals the 4WD control module when the operator activates the brake pedal.

Digital Transmission Range (TR) Sensor

The digital TR sensor is located on the outside of the transmission near the transmission shift cable attachment. The digital TR sensor completes the start circuit in PARK and NEUTRAL, the back-up lamp circuit in REVERSE and the neutral sense circuit (4WD) in NEUTRAL. The digital TR sensor also sends a digital output signal to the PCM indicating the manual lever position.

Throttle Position (TP) Sensor

The TP sensor is located on the throttle body. The sensor provides throttle position information to the powertrain control module (PCM). The PCM converts the throttle position signal to a pulse width modulated (PWM) signal, and sends it to the 4WD control module to control and adjust the transfer case clutch duty cycle.

Front and Rear Output Shaft Speed (OSS) Sensors

The externally mounted OSS sensors are located at the rear of the transfer case. The sensors provide the 4WD control module with front and rear driveshaft speeds to control and adjust the transfer case clutch duty cycle.

On vehicles equipped with stability assist, the OSS sensors are present, but not used. The front and rear drive shaft speeds are transmitted to the 4WD control module from the stability assist module. The stability assist module receives the necessary signal from the wheel speed sensors.

Vehicle Speed Sensor (VSS)

The Anti-Lock Brake System (ABS) provides the 4WD control module with the vehicle speed information to control and adjust the transfer case clutch duty cycle.

4WD Control Module

The 4WD control module, located behind the glove compartment, controls the operation of the transfer case in response to the inputs from the shift motor, MSS, BPP switch, digital TR sensor, throttle position output from the PCM, front and rear OSS (on non-stability assist vehicles), stability assist module (if equipped) and the VSS.

Range Function

Note. At zero throttle, the duty cycle remains low.

In the 4x4 Low range, with throttle input, the transfer case electromechanical clutch looks at the front and rear driveshafts for maximum 4x4 traction. The transfer case shift motor rotates the shift cam to move the reduction shift fork to the 4x4 Low range position. This low range shift, accomplished through a planetary gear set, changes the torque to the drive shaft from 1:1 to 2.48:1 ratio.

In the 4x4 High range, with throttle input, the 4WD control module signals the transfer case electromechanical clutch to lock the front and rear driveshafts for maximum four wheel drive traction. Never use the 4x4 High range or the 4x4 Low range when driving on dry or merely wet pavement. Use 4x4 High range or the 4x4 Low range only for driving off-road or in severe winter weather.

Possible Causes

  1. MSS
  2. 4WD control module
  3. 4WD indicator
  4. circuit 359 (GY/RD)
  5. circuit 780 (DB)
  6. transfer case electric clutch
  7. circuit 779 (BR)
  8. circuit 976 OG
  9. circuit 357 (YE/WH)
  10. circuit 3126 (TN/WH) (stability assist only)
  11. circuit 3125 (RD/YE) (stability assist only)
  12. circuit 774 (LG) (non-stability assist vehicles)
  13. OSS (non-stability assist vehicles)
  14. circuit 236 (BK/LG)

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Scheme 108: Testing
Scheme 108: Testing

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  1. circuit 972 (BK/WH)
  2. circuit 1203 (BK/LB)
  3. 4WD control module
  4. circuit 693 (OG)

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Scheme 121: Testing
Scheme 121: Testing

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Scheme 122
  1. digital transmission range (TR) sensor
  2. circuit 463 (RD/WH)
  3. circuit 976 (OG)
  4. brake pedal position (BPP) switch
  5. circuit 511 (LG)
  6. mode select switch (MSS)
  7. circuit 784 (LB/BK)
  8. circuit 464 (BK/PK)
  9. 4WD control module
  10. circuit 762 (PK/YE)
  11. circuit 763 (WH)
  12. circuit 764 (BN/WH)
  13. circuit 770 (OG/WH)
  14. circuit 771 (YE/WH)
  15. transfer case shift motor
  16. transfer case clutch
  17. circuit 777 (YE)
  18. circuit 778 (OG)
  19. transfer case shift shaft
  20. transfer case gearmotor encoder assembly

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Scheme 123: Testing
Scheme 123: Testing

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Scheme 135: Transfer Case Draining and Filling
Scheme 135: Transfer Case Draining and Filling
  1. Remove the fill plug and check the fluid level. If the fluid is below the proper level, fill the transfer case with automatic transmission fluid.

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Scheme 136: Material
Scheme 136: Material

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Scheme 137: Removal and Installation
Scheme 137: Removal and Installation

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  1. Remove the upper radiator fan shroud. For additional information, refer to «ENGINE COOLING»(ref-194047) .
  2. Remove the rear driveshaft. For additional information, refer to «DRIVELINE SYSTEM»(ref-194029) .
  3. Remove the front driveshaft. For additional information, refer to «DRIVELINE SYSTEM»(ref-194029) .
  4. Remove the four bolts and the skid plate, if equipped.
  5. Drain the fluid if the transfer case is to be disassembled. For additional information, refer to «TRANSFER CASE DRAINING AND FILLING»(ref-194050-S17414734442005092600000) .
  6. Remove the RH and LH heat shield-to-crossmember bolts.
  7. Remove the components in the order indicated in the following illustration and table.
  8. To install, reverse the removal procedure.

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