Transfer Case - Vehicles With: Twin Speed Transfer Case (G2130984): 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 two side gears. One 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, via 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 rearwards 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 and, via 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, via the shifting sleeve, to the differential housing where it is split between the two side gears. One 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, via the drive chain, to the front output flange. The vehicle will remain in the selected range unless the driver requests a change, for example it will not automatically revert to high range following an ignition off/on sequence.

Range Change Procedure 

Range change can be requested at any time while the engine is running. If the conditions are not met for range change, the Instrument Cluster (IC) will display the appropriate message in the message center. The message guides the driver to complete the range change and the low range warning indicator will flash. Once Neutral (N) is selected in the Transmission Control Switch (TCS), the TCS will be 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
• If the first attempt was unsuccessful.

Default/Limp-home Strategy 

If a fault occurs with the transfer case, the Transfer Case Control Module (TCCM) or one of the required input signals (for example vehicle speed signal), the TCCM records a Diagnostic Trouble Code (DTC). The TCCM will respond appropriately to provide the highest level of system capability under the specific fault conditions. The following fault states are possible:

Fault state	System response	Driver warning
Clutch control not available due to an over temperature	A driver warning message is displayed. The tractive capability or off-road capability of the vehicle is reduced temporarily.	Warning indicator and/or 'Traction Reduced' message in message center
Clutch control not available due to a permanent fault	A driver warning message is displayed. The tractive capability or off-road capability of the vehicle is reduced.	Warning indicator and/or 'Traction Reduced' message in message center
Transfer case is in Neutral	If engine starts while the transfer case is in Neutral (N) and the automatic transmission is not in N. The Transfer Case Control Module (TCCM) sets a warning message and attempt to engage High range when N is selected on the Transmission Control Switch (TCS).	Flash low range indicator and 'High Range Requested: Select Neutral (N) for Range Change' message
Transfer case stuck in Neutral	As the transfer case is stuck between high and low range resulting in no drive to wheels, the Electric Park Brake (EPB) will automatically apply when Park position in the TCS is selected or engine is turned off.	Flash low range indicator plus 'Loss of Drive' message
Range change not available	A driver warning message is displayed and range change is not performed. Range change is not available due to:	'Range Change not Available' on instrument pack if a range change is requested
	A fault in system
	The supply voltage to TCCM is below 10.5 V
	The oil temperature in the transfer case is below -30°C (-22°F).
No functional degradation	A signal fault or Diagnostic Trouble Code (DTC) may be logged but no customer symptom if a back-up signal is available and used.	None

If a component in the twin speed transfer case or the Transfer Case Control Module (TCCM) is overheated, the TCCM set a Diagnostic Trouble Code (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 will not displayed.

When a range change is completed in ambient temperature below 0°C (32°F), TCCM inhibits the next range change for 1 minute. This is to protect the TCCM and is design intent. 'Range change not available' message will be displayed if a range change is requested within this 1 minute without DTC.

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

• If the twin speed transfer case is in Neutral (N) and TCCM is in recovery mode
• Transmission Control Switch (TCS) is not in N position which is required for range change.

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

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