Transfer Case: Description and Operation

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TRANSFER CASE ELECTRONIC SHIFT ON - BOARD DIAGNOSIS

Principles of Operation

The electronic shift on the fly (ESOF) system is an electronic shift system that allows the operator to choose between 2 different 4-wheel drive modes as well as 2-wheel drive. The operator can switch between 2WD and 4x4 HIGH mode at speeds up to 88 km/h (55 mph). To engage or disengage 4x4 LOW range, the vehicle speed must be less than 5 km/h (3 mph) and the transaxle must be in NEUTRAL (or the clutch pedal pressed in manual transaxle vehicles).
When the mode select switch (MSS) on the instrument panel is turned, the 4WD control module powers the transfer case shift motor. When the shift motor reaches the desired position, as determined by the contact plate position inputs to the 4WD control module, power to the shift motor will be removed.

Transfer Case 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 4x4 LOW range is selected.
Digital Transmission Range (TR) SensorThe digital transaxle range (TR) sensor completes the start circuit in PARK and NEUTRAL, the back-up lamp circuit in REVERSE and the neutral sense circuit in NEUTRAL. The digital TR sensor also sends a digital output signal to the PCM indicating the manual lever position.

Feature Inputs:
- MSS
- Wheel speeds (via CAN communication)
- Contact plate position inputs A, B, C, D (grounded when closed, open circuit when open)
- Digital TR sensor

Feature Outputs:
- Transfer case shift motor
- Instrument cluster indicators (via CAN communication)
- 4WD mode (via CAN communication)

Neutral Tow

The neutral tow feature is a program embedded in the 4WD control module, which must be activated by a dealer technician. The neutral tow feature disengages the wheels from the powertrain by shifting the transfer case to the NEUTRAL position. This allows the vehicle to be towed with all 4 wheels on the ground. To activate the neutral tow feature, the dealer technician must access the 4WD control module through the IDS or equivalent tester and data link connector. Once communication is achieved, the technician can request the neutral tow feature be enabled. The technician must also install the neutral tow indicator lamp in order for the feature to be activated.
Feature inputs:

- MSS
- Contact plate position inputs A, B, C, D
- Vehicle speed signal (VSS)
- Door ajar switch (battery voltage when door is closed, grounded circuit otherwise)
- Digital TR sensor
Feature outputs:

- 4WD shift motor outputs
- Neutral tow indicator lamp

- If the network test passes, retrieve and record continuous memory diagnostic trouble codes (DTCs).