Sierra Classic 2500 4WD V8-6.0L (2007)
Four Wheel Drive Selector Switch: Description and Operation
Transfer Case Description and Operation
Transfer Case Shift Control Switch
The NVG 263 transfer case features a three button shift control switch located on the instrument panel. When the ignition is in the RUN position, the
transfer case shift control module (TCCM) starts monitoring the transfer case shift control switch to determine if the driver desires a new mode/gear
position. At a single press of the transfer case shift control switch, the lamp of the new desired position begins flashing to inform the driver that the
TCCM has received the request for a new mode/gear position. The lamp continues to flash until all shifting criteria has been met and the new
mode/gear position has been engaged. Once the new mode/gear position is fully active, the switch indicator for the new position remains ON
constantly. In the event that the TCCM can not or will not complete the shift, the indicator returns to the previously selected position; this is a Transfer
Case Shift Control Switch Indicator Flashes, then Returns to Previous Mode condition.
The NVG 263 transfer case provides the driver with 4 manual mode/gear positions:
^
2HI - 2 Wheel Drive high range
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4HI - 4 Wheel Drive high range
^
4LO - 4 Wheel Drive low range
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NEUTRAL
The driver may choose to select any of these mode/gear positions while driving the vehicle. However, the transfer case will not allow a shift into or out
of 4LO unless the following criteria has been met:
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The ignition switch is in RUN.
^
The automatic transmission is in PARK or NEUTRAL - clutch depressed on manual transmissions.
^
The vehicle speed is below 5 km/h (3 mph).
This transfer case also has a NEUTRAL position. A shift to the NEUTRAL position allows the vehicle to be towed without the rear axle rotating the
transmission output shaft. NEUTRAL position may be obtained only if the following criteria has been met:
^
The ignition switch is in RUN.
^
The automatic transmission is in PARK or NEUTRAL - clutch depressed on manual transmissions.
^
The vehicle speed is below 5 km/h (3 mph).
^
The transfer case is in 2HI mode.
Once these conditions have been met, press and hold both the 2HI and 4LO buttons for 10 seconds. When the system completes the shift to
NEUTRAL, the red NEUTRAL lamp illuminates.
A shift to the NEUTRAL position allows the vehicle to be towed without rotating the transmission output shaft. In the NEUTRAL position, the rear
propeller shaft rotates the transfer case rear output shaft, in turn rotating the oil pump, thus providing constant lubrication during towing. This
NEUTRAL position is a 4WD NEUTRAL, meaning the front and rear outputs of the transfer case are engaged as though in 4HI. With a disengaged
front axle, there is no power flow to the front wheels, thus allowing towing with the front wheels off the ground or flat towing without driveline
binding.
The NVG 263 transfer case is available in 2 variations, depending on the engine and transmission configurations. The variations allow the transfer
case to handle different torque loads. When servicing the transfer case, it is important to understand which variation is being serviced because of the
difference in parts.
