Land Rover Defender: Operation

High range operation

In high range, the torque output from the automatic transmission is passed to the transfer case input shaft. The position of the shifting sleeve couples the input shaft directly to the transfer case housing. The differential splits the torque between the 2 side gears. The 1 side gear is connected by splines and passes the torque to the rear output flange. The second side gear is connected to the chain drive sprocket and passes the torque, through the drive chain, to the front output flange.

Low range operation

In low range, the torque output from the automatic transmission is passed to the transfer case input shaft. The shifting sleeve is moved rearward and connects the planetary ring gear to the transfer case housing. The torque from the automatic transmission is now directed through the sun gear of the epicyclic gearset. The torque through the pinion gears and pinion gear shafts, into the planetary carrier. The annulus gear of the epicyclic gearset is secured inside the casing and generates the low range ratio of 2.93 : 1.

The torque is then passed, through the shifting sleeve, to the differential housing where it is split between the 2 side gears. The 1 side gear is connected by splines and passes the torque to the rear output flange. The second side gear is connected to the chain drive sprocket and passes the torque, through the drive chain, to the front output flange. The vehicle remains in the selected range unless the driver requests a change. The range not automatically reverts to high range following an ignition OFF/ON sequence.

Range change procedure

NOTE: Changing from high range to low range can be performed only when the vehicle is stationary.

Range change can be requested at any time while the engine is running. When the conditions are not met for range change, the IPC displays the appropriate message in the message center. The message guides the driver to complete the range change and the low range warning indicator flashes. When Neutral is selected in the TCS, the TCS is locked until the range change is completed.

The range change process can take several seconds to complete after a request is accepted. The actual time is dependent on a number of factors including:

• Transfer case temperature is out of range.
• Component wear.
• When the first attempt was unsuccessful.

Default/Limp-home strategy

The TCCM records a Diagnostic Trouble Code (DTC) when a fault occurs with the transfer case. The TCCM also records a DTC when 1 of the required input signals (for example, vehicle speed signal) is not right. The TCCM responds appropriately to provide the highest level of system capability under the specific fault conditions. The following fault states are possible:

When a component in the twin speed transfer case or the TCCM is overheated, the TCCM set a DTC. The TCCM opens the clutch and 'Traction reduced' warning message is displayed. When the component is cooled down sufficiently, the clutch control is re-activated and the message is not displayed.

When a range change is completed in ambient temperature below 0ºC (32ºF), the TCCM inhibits the next range change for 1 minute. The function is to protect the TCCM and is design intent. 'Range change not available' message is displayed when a range change is requested within this 1 minute without DTC.

The TCCM has a recovery strategy from failures of transfer case Neutral. When engine starts or it attempts to reengage high range first and subsequently low range when high range engagement is still not achieved. A 'Select Neutral for Range change' message is displayed:

• When the twin speed transfer case is in Neutral and the TCCM is in recovery mode.
• The TCS is not in Neutral position which is required for range change.

When range change is requested and the requested range is not achieved, the TCCM attempts to re-engage the previous range. When a requested range not achieved while vehicle is stationary, another range change request is recommended after vehicle moves a short distance. Another range change request is recommended after switch ignition OFF for the minimum 1 minute and start the engine.

The TCS is locked in Neutral position while the TCCM is performing range change. The function is a normal function and this also applies to a range change during the recovery mode.

DIANGOSTICS

The TCCM records any DTCs and related data. The DTCs and related data are read using the Jaguar Land Rover (JLR) approved diagnostic equipment.

The JLR approved diagnostic equipment enables certain components to be activated and also read live data.

CONTROL DIAGRAM

CONTROL DIAGRAM - TCCM

A = HARDWIRED:
U = PRIVATE CAN BUS:
AX = FLEXRAY:
BA = HIGH SPEED (HS) CAN HUMAN MACHINE INTERFACE (HMI) SYSTEMS BUS.

1. TCCM
2. FCIM - High/Low range selection switch
3. HVAC control module
4. BCM/ GWM
5. Transmission Control Module (TCM)
6. Transfer case actuator
7. Ground
8. Power
9. High/Low range position sensor

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