Four wheel drive wont engage the decoder motor is working on the transfer case and i replaced the vacum switch on the front axel thanks Bob

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 .

Remove the transfer case and strip it down,wash it out and replace whatever is worn.
330,000 miles is unrealistic
Your chain is worn and stretched for sure, and rattling and may be cutting into the case.
Don't install another salvage yard unit, unless you can not repair yours. Then strip down whatever you purchase, and go thru it also.

if the actuateor is vacumed,you might have have a hose that came off or it has a split in it somewhere,check that.or if you have posilock hubs one or both may be wore out or lacking grease,they are easy to remove,just a hex wrench and snapring pliers is all you need,remove and inspect for obvious sighns of wear.

May need to replace the switch itself. Most new vehcile are all electronically engaged. Replace the switch. Cheap fix compared to going into the transfer case first.

Normal thing that happens as long as onone (worked) on it, is the vacume hose going to the engage sevevo under the battery box has fell of on either end or is brocken on the way there. Then the once or now leaky battery acid ate up this same servo. then the cable going to the front axel breaks sticks falls off or even someone needing one climbed under your truck while parked somewhere to get one to replace their brokeen one now you don't have one then theaxel engage arm or gearset is damaged

If you can have the codes scanned in your vehicle it would be very helpful to you. If you have a code for the encoder motor sensor or the encoder motor itself on the side of the transfer case, this is where i would begin, quite common with the push button 4 wheel drive. Thanks for using fixya!! good luck

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

that vacume line goes back to the transfer case, the end that goes behind the motor hooks to a steel tube so it does not get hot from the exhaust., my guess it should be hooked up so it will feed vacume to the vacume ball so it can lock in the axels. if you start the car and shift into 4 wheel drive and listen under hood you should hear a hissing sound, that is vacume, if you can't hear it there, you may have to craw under the right side to hear it, probably came unhooked underneith the car

Theres a vacume dash pot under the battery box. It pulls a cable that engages the front diff. Put the vacume line and you'll have lights and four wheel drive. (it happened to my blazzer)

Hi, I had a 88 cherokee, had no 4 wheel drive, the vac. motor u r referring to engages the 4x4. Mine vac motor was replaced, fixed the problem.