No four wheel drive

Which of these does your vehicle have ?

Transfer Case - NVG 233-NP1 (Two Speed Selectable)
Transfer Case - NVG 136-NP4(One Speed Automatic)

The New Venture Gear NV233 is an electronic shift transfer, with the following three modes of operation, Two-wheel drive high range, Four-wheel drive high range, Four-wheel drive low range. The gear reduction for low range is provided by a planetary gear set. The floor-mounted shifter has been eliminated. A switch, located on the upper right side of the instrument panel, is used to select the operating range. The indicator lamps on the switch show the current mode of operation. When the four-wheel drive has been selected, the four-wheel drive indicator lamp on the switch is designed to turn on when the front axle has engaged.


Automatic Transfer Case
The single speed automatic transfer case system shifts automatically from rear wheel drive to four wheel drive when the transfer case shift control module (TCSCM) senses the difference in rotation speed of the front propeller shaft and the rear propeller shaft . Two vehicle speed sensors, one located at the rear output shaft area of the transfer case, and the other, located at the front output shaft area of the transfer case, send front and rear propeller shaft rotation speed information to the TCSCM.
When the front and rear output shaft rotations remain the same, the TCSCM sends pulse width modulation signals to the encoder/motor to keep the transfer case in rear wheel drive. When the front and rear output shafts rotations are different, the shift control module sends pulse width modulation signals to the encoder/motor to engage the transfer case into four wheel drive.
The system will automatically transfer a percentage of torque to either the front or rear axles as required to stop all wheel slip. When the front and rear output shafts rotations return to the same speed rotation, the shift control module sends pulse width modulation signals to the encoder/motor to position the transfer case back into rear wheel drive.
When the transfer case is engaged into four wheel drive, a lamp indicator on the instrument cluster will light. The automatic transfer case system is completely automated, no transfer case control button switching system is required.

Do you know what diagnostic trouble code's are ?

DTC C0300 Rear Speed Sensor Malfunction
DTC C0305 Front Speed Sensor Malfunction
DTC C0308 Motor A/B Circuit Low
DTC C0309 Motor A/B Circuit High
DTC C0310 Motor A/B Circuit Open
DTC C0315 Motor Ground Circuit Open
DTC C0374 General System Malfunction
DTC C0376 Front/Rear Shaft Speed Mismatch
DTC C0550 ECU Malfunction
DTC C0611 VIN Information Error
DTC C0895 Device Voltage Malfunction

Not OBD2 engine code's .

Which do you have ?
Transfer Case - NVG 236 (Two Speed Automatic)
Transfer Case - NVG 233-NP1 (Two Speed Selectable)
The NV236 transfer case is an automatic transfer case with three drive ranges. Shifting from rear wheel drive to four wheel drive is done automatically when the transfer case shift control module receives wheel rotating slip information from the speed sensors. The transfer case shift control module then engages the transfer case motor/encoder to position the transfer case from rear to four wheel drive. When the transfer case shift control module receives information that the wheel rotation is the same on both axles, the transfer case shift control module sends position information to the motor/encoder to put the transfer case back into rear wheel drive. The three drive ranges are 2HI, 4HI, and 4LO. The 2HI position is for normal driving with the rear wheels pushing the vehicle. The 4HI, position is for driving through sand, snow, mud, gravel, or heavy rain at normal or slightly below normal speeds. The 4HI engages the front axle to allow for four wheel drive. The front axle is pulling the vehicle, and the rear axle is pushing the vehicle. The 4LO range is used for off road driving, heavy snow, deep mud, or shallow fording. The 4LO is similar to the 4HI except that the gearing in the transfer case is set for low speed and high torque. The NV236 is manufactured at Syracuse New York by New Venture Gear a division of New Process Gear for General Motors.
Is the switch light on or flashing ? If you have automatic 4x4 there are several DTC'S that can set >
DTC B2725 ATC Mode Switch Circuit Malfunction DTC C0300 Rear Speed Sensor Malfunction DTC C0305 Front Speed Sensor Malfunction DTC C0308 Motor A/B Circuit Low DTC C0309 Motor A/B Circuit High DTC C0310 Motor A/B Circuit Open DTC C0315 Motor Ground Circuit Open DTC C0323 T-Case Lock Circuit Low DTC C0324 T-Case Lock Circuit High DTC C0327 Encoder Circuit Malfunction DTC C0362 4LO Discrete Output Circuit High DTC C0367 Front Axle Control Circuit High DTC C0374 General System Malfunction DTC C0376 Front/Rear Shaft Speed Mismatch DTC C0387 Unable to Perform Shift DTC C0550 ECU Malfunction DTC C0611 VIN Information Error

No 4X4 switch on the instrument panel ?
Automatic Transfer Case
The single speed automatic transfer case system shifts automatically from rear wheel drive to four wheel drive when the transfer case shift control module (TCSCM) senses the difference in rotation speed of the front propeller shaft and the rear propeller shaft . Two vehicle speed sensors, one located at the rear output shaft area of the transfer case, and the other, located at the front output shaft area of the transfer case, send front and rear propeller shaft rotation speed information to the TCSCM.
When the front and rear output shaft rotations remain the same, the TCSCM sends pulse width modulation signals to the encoder/motor to keep the transfer case in rear wheel drive. When the front and rear output shafts rotations are different, the shift control module sends pulse width modulation signals to the encoder/motor to engage the transfer case into four wheel drive.
The system will automatically transfer a percentage of torque to either the front or rear axles as required to stop all wheel slip. When the front and rear output shafts rotations return to the same speed rotation, the shift control module sends pulse width modulation signals to the encoder/motor to position the transfer case back into rear wheel drive.
When the transfer case is engaged into four wheel drive, a lamp indicator on the instrument cluster will light. The automatic transfer case system is completely automated, no transfer case control button switching system is required.

Do you know what DTC'S - diagnostic trouble code's are ?
Auto part stores can't read these , your best bet take it to a qualified repair shop . One that has the knowledge an diagnostic equipment .
DTC C0300 Rear Speed Sensor Malfunction
DTC C0305 Front Speed Sensor Malfunction
DTC C0308 Motor A/B Circuit Low
DTC C0309 Motor A/B Circuit High
DTC C0310 Motor A/B Circuit Open
DTC C0315 Motor Ground Circuit Open
DTC C0374 General System Malfunction
DTC C0376 Front/Rear Shaft Speed Mismatch
DTC C0550 ECU Malfunction
DTC C0611 VIN Information Error
DTC C0895 Device Voltage Malfunction
Without proper factory service an repair info. an diagnostic tools

try checking your silinoid. Some of these newer vehicles have an electronic silinoid that is responsible for engaging your transfer case into four wheel drive. Also if you have push button or shift on the fly four wheel drive your switch may have gone bad. I hope this helps you.

It's the transfer case motor.I had the same problem exactly and replaced, now it works great. Part is about $100.00 ( aftermarket ) .Ifyou are going to replace yourself you will have to remove front drive shaft and remove yoke from transfer case with an impact wrench for clearance to remove transfer case motor . When you put the new transfer case motor in make sure you line up slot with grove in transfer case motor. Good Luck.

Was the transfer case fluid changed every 50K miles? This very important on these trucks. The Transfer Case Control Module (TCCM) could be at fault, especially since you have no lights on the selector switch. Is the Service 4x4 light on? When you switch from 2H to any of the 4 wheel drive selections, do you hear any actuator noises coming from under the truck?

Is the 4 wheel light flashing on the dash. If so the problem could be in the computer if it is electronic 4 wheel drive. It can also be the motor on the transfer case or the switch on the dash. You can check the switch on the dash and see if you are getting power to it and out of it. Then you can check and see if you are getting power to the motor on the transfer case. If you are getting power in the switch but none coming out of it when switch to the 4 wheel drive position it is the switch but if you are and are getting power down to the motor on the transfer case it is the motor on the transfer case. If you are not getting power to the switch then it is in the control computer for it mounted in the dash behind the radio.

the motor on the back of the transfer case may be stuck knock on the motor lightly with a hammer when switching the the switch May need a motor

DID YOU CHECK THE MOTOR IN THE FRONT AXLE AS WELL AS THE ONE IN THE TRANSFER CASE GOOD LUCK

The four wheel drive systems in these vehicles are simple. The push button controls the four wheel drive computer. The computer tells the encoder motor (on transfer case) to shift. When the transfer case shifts there is a vaccum switch on the transfer that is activated which sends vaccum to the accuator under the battery. The accuator pulls a cable to lock the front axle in. This covers all s series trucks and suv's with push button four wheel drive but not with auto or all wheel. Now to answer some questions. If your push button is lit up but will not go in to four high you should try to reset the four wheel drive computer. To reset pull the courtesy light and atc fuses for sixty seconds install fuses then cycle key on and off 5 times. If your transfer case shifts but your front end does not lock in check for vaccum at the switch on the transfer case in and out. If no vaccum out replace switch motormite number 49315 at parts store. If you have vaccum out check accuator.