Transter case problems

I have run into to this problem many times on these trucks, i have seen your problem and also where the 4wd high light wont work but 4wd low and 2wd work fine and the 4 wheel drive works fine. on your truck i will bet its the transfer case selector motor.
the motor is what turns the lights on when in the selected mode which goes through the 4wheel module under the dash, this sounds like a bad selector motor and that where i would start. this motor is located on the transfer case, it bolts to the rear of it.here is a picture of it to help you locate it. good day.

Operationally vacuum shifts the front axle between 2WD and 4WD mode. The GEM ( Generic Electronics Module ) applies ground to the solenoid needed for the mode selected on the switch ( for ESOF ) or when the transfer case shift lever is moved ( MSOF ).The contact plates in the transfer case signal the GEM that the transfer case is engaged, and the Vacuum solenoids need to be activated ( either 2WD to 4WD or 4WD to 2WD ).

Lift and support the front of the truck so the front wheels are off the ground ( take safety precautions, chock wheels, jack stands, etc )
Key on, engage 4x4 and try to turn the front drive shaft.
- If it turns it is a problem with the transfer case.
- If it doesn't it is a front axle engagement problem ( this is what you seem to have, the transfer case is engaged and will drive the front shaft mine was a key on engine off test ).

- If the front drive shaft does not turn :
•With the truck running ( with front wheel back on the ground ), switch from 2WD to 4WD and back again, the vacuum shift motor should move the lever on the front axle.

-- If the vacuum shift motor does not move:
1.Check for vacuum on the lines while shifting between modes. Pink vacuum line is 2WD mode, Light Blue vacuum line is 4WD.
2.Check the fuses for the 4WD system and the solenoids.
3.Check the vacuum lines from the vacuum shift motor to the solenoids on the firewall.

4.Check the vacuum lines from the solenoids to the vacuum reservoir box behind the battery.
5.Check the vacuum reservoir box for cracks.
6.Typical solution is the vacuum lines ( to the solenoids or to the vacuum shift motor ) are cracked or the vacuum shift motor has a cracked diaphragm and has water in it.
7.Could be the shift plate contacts in the transfer case are corroded / not making good contact, and not activating the solenoids.


Usually the case is cracked vacuum lines from the solenoids, the next common is a cracked vacuum reservoir box, and 1 time I have seen the mount for the vacuum disconnect motor broken ( motor floating free so it could not push against the axle )

if you had the rear wheels still on the ground in 4WD and it never drove the vehicle off the jacks or stands , you have a problem in the transfer case
in other words the transfer case is not selecting WD

There are 2 actuators, one controls the transfer case, the other controls the front axel. If you have an assistant, you can tell which one isn't doing it's job by looking from the outside under the truck and see if the front drive shaft is turning when the truck moves. If it does then it's the axel actuator which is located on the right side of the housing, if it doesn't turn, it's the transfer case that's the problem. (If that's the case, then be sure of the problem as it could be number of things associtated with this system and can be very costly guessing). The best way to find out why the transfer case isn't engaging is with a good scanner and read the system's controller.

There may be vacuum lines running down to the hubs. If so check them for vacuum when engaging and dis-engaging 4 wheel. If you can't feel any vacuum, trace lines, and check for leaks.

sounds like it might be an encoder moter, but the best thing you can do is take it to a good transmission shop so they can hook up their reader and find out for sure

THE TRANSFER CASE MOTOR IS NOT WORKING TO INGAGE 4 WHEEL DRIVE. CHECK WITH DOOR OPEN WHEN YOU PUSH 4 WHEEL SWITCH YOU SHOULD HEAR MOTOR INGAGE 4 WHEEL DRIVE. IF YOU HEAR MOTOR BUT STILL NO 4 WHEEL DRIVE THE GEAR ON MOTOR COULD BE DAMAGED. REPLACE TRANSFER CASE MOTOR.

the transfer case module is bad it is bolted to transfer case above front drive shaft

no it should not spin when is in 2wd thanks

Chain. And they very rarely break. Have you jacked up the rear wheels and put it in 4wd to see if the front shaft is turning with the rear shaft. This will determine if it is a transfer case problem or a front differential actuator problem.