Part 3
Four-Wheel Drive Systems - 4.2L/4.4L (Part 3)TRANSFER BOX CONTROL MODULE
TRANSFER BOX CONTROL MODULE (PART 1):
The transfer box control module controls the high/low 'shift-on-the-move' actuation and the multi-plate clutch actuation.
The control module is located in the E-box, next to the Engine Control Module (ECM).
The control module is connected to the Controller Area Network (CAN) bus and controls transfer box operation using CAN messages from other control modules on the network.
The control module memorizes the position of the transfer box motor when the ignition is switched off.
The transfer box control module uses the same actuator to control both range change function and application of center differential locking torque. The module uses position feed back from the actuator to provide smooth range changing capability and graduated application of locking torque appropriate for the current driving conditions. Range change can be carried out while moving providing the transmission is in neutral and the vehicle is below the speed necessary for the requested range change.
The control module uses three connectors for all inputs and outputs. It receives a permanent power supply via a 30A fuse located in the Battery Junction Box (BJB), and an ignition supply via fuse 33 in the Central Junction Box (CJB).
The control module uses a series of programmed shift maps to control the synchronization speed and ensure that a maximum shift time of approximately one second is achieved.
If the control module is replaced, T4 must be connected to the vehicle and the transfer box control module self-calibration procedure must be performed. This procedure must also be performed if the transfer box motor assembly is replaced.
Default/Limp-home Strategy
If a fault occurs with the transfer box, the transfer box control module or one of the required input signals i.e. road speed signal, the control module records an error code and will respond appropriately to provide the highest level of system capability under the specific fault conditions. These fault states are possible:
TRANSFER BOX CONTROL MODULE (PART 2):
If a driveline over temperature condition has occurred, after the driveline has been allowed to cool, clutch control will be re-enabled and the warnings will disappear. There is no need to seek service assistance following an over temperature event.
If clutch control or range change is not possible due to a permanent fault the driver must seek service assistance at the earliest opportunity.
If the system suffers a fault, which causes the transfer box to fail in neutral, the control module is designed to continue attempting to engage the requested range or return to its original range for a fixed number of attempts. If this has not been successful and the low range lamp is still flashing the driver should bring the vehicle to a halt and attempt the range change again while stationary. If this does not work after a number of attempts, key off for 30 seconds, restart engine and request range change again while stationary. The driver must seek service assistance at the earliest opportunity.
Transfer Box Control Module Pin Out Details
Connector 1 - C1856:
Connector 2 - C1854:
Connector 3 - C1855:
TRANSFER BOX CONTROL MODULE INPUTS
The transfer box control module receives these inputs:
^ Range change selection switch
^ High/low position sensor
^ Transfer box actuator motor temperature
^ Transfer box actuator motor position sensor
^ CAN bus messages.
CAN Bus Messages
The CAN bus is a high speed broadcast network connected between various vehicle control modules. The CAN network carries an extensive list of messages between the different control modules enabling more sophisticated control with reduced complexity. Data on the network is packaged for efficient communication and prioritized according the urgency and importance of the messages. The bus comprises two wires, which are twisted together to minimize electromagnetic interference (noise) produced by the CAN messages.
The transfer box control module is connected on the CAN bus and controls transfer box operation using CAN messages from other control units on the network. Wheel speed, vehicle acceleration, engine torque and speed, gear information, from the transmission, temperature information, car configuration, axle ratios and Terrain Response(TM) mode inputs, are some of the main signals received by the control module.
In the event of a CAN bus failure these symptoms may be observed:
^ Shift from high to low or low to high inoperative
^ Instrument cluster low range warning lamp inoperative
^ Warning messages or lamps displayed in instrument cluster.
Range Change Selection Switch
Range Change Selection Switch (Part 1):
The range change selection switch is located behind the main transmission selection lever, in the center console. The switch is a 2-position sprung device. The driver pulls the lever backwards to select a range change, the transfer box will then change to the other available range. The same direction is used for both high and low range.
The switch comprises a housing, which provides the location for a sliding contact. When the switch is moved to the range change position, it completes a momentary connection to 12V with the micro-switch located at the end of the range change selection switch.
The transfer box control module receives this momentary signal and attempts a range change. The switch will return to its normal position when released.
High/Low Position Sensor
Range Change Selection Switch (Part 2):
High/Low Position Sensor:
The high/low position sensor converts the pivotal movement of the high/low fork into a PWM signal on the input. The PWM signal of the position sensor differs between high range and low range. The control module checks this signal and informs the driver, via the instrument cluster and the range change selection switch LED's, if a range change is in progress or has been completed.
The high/low position sensor is connected to the transfer box control module via a three-pin connector.
TRANSFER BOX CONTROL MODULE OUTPUTS
The transfer box control module sends these outputs:
^ CAN bus messages
^ Key interlock solenoid
^ High/low range change LED
^ Transfer box motor
^ Solenoid.
CAN Bus Messages
The control module also sends messages via the CAN bus to tell other control modules on the network, the status of the transfer box. The high/low status, clutch torque and default mode status are some of the main signals sent out by the transfer box control module.
Key Interlock Solenoid
The transfer box control module is able to send a signal to the key interlock solenoid. This signal locks the key in the ignition barrel to prevent it from being removed if the transmission is not in the 'Park' position.
Transfer Box Motor
Transfer Box Motor:
The transfer box motor provides the necessary movement to perform the high/low range change and the multi-plate clutch actuation. The motor is located on the rear casing assembly and secured with four bolts.
The motor is a PWM controlled, DC motor with an integrated worm gear reduction drive. It is connected to the transfer box control module with an eight-pin connector; the power supply of the motor is maintained through two large diameter cables on the motor connector. An internal position sensor checks the rotational movement of the motor.
There is a temperature sensor located within the motor housing.
Solenoid
Solenoid:
The solenoid switches the power flow on the actuation system between high/low range change mode and clutch control mode. When the solenoid is energized, the solenoid pin deploys and activates the clutch control mode. When the solenoid is de-energized, the internal spring rejects the solenoid pin and activates the high/low range change mode.
NOTE: In order to replace the solenoid in service, the solenoid must be energized using T4.
The solenoid is connected to the transfer box control module with a two-pin connector.
Status Indication
Instrument Cluster (Part 1):
Instrument Cluster (Part 2):
The low range status indicator will take the form of a mountain symbol and has this logic:
^ Lamp on = low range
^ Lamp off = high range
^ Lamp flashing = range change in progress/range undefined/range fault.
There will also be a message displayed in the message center, which will inform the driver of any faults with the transfer box.
This table shows the messages that can be displayed in the message center relating to the transfer box:
