I recommend you engage 4x4 low and leave the vehicle running then raise the complete front end and see if the front hubs are engaging the halfshafts by turning the tire.
The transfer case is equipped with an electromagnetic clutch which is located inside the case. This clutch is used to synchronize the front driveline. When the mode select switch (MSS) on the instrument panel is turned, the 4x4 module (PCM) activates the electromagnetic clutch and powers the transfer case shift motor. When the shift motor reaches the desired position, as determined by the contact plate position inputs to the 4x4 module (PCM), power to the shift motor will be removed. When the transfer case front and rear output shafts are synchronized, the spring loaded lockup collar mechanically engages the mainshaft hub to the drive sprocket. Finally, the front axle integrated wheel ends (IWEs) are engaged and the electromagnetic clutch is deactivated
Integrated Wheel End (IWE) System
The integrated wheel end (IWE) system contains the following:
- Vacuum reservoir
- IWE solenoid
- IWEs (spring loaded vacuum hubs)
- Vacuum hoses
- Check valve
The IWE system uses vacuum hubs that engage the front wheel hubs to the front halfshafts or disengage the front wheel hubs from the front halfshafts.
The IWE solenoid receives engine vacuum from the vacuum reservoir.
When the 4-wheel drive system is in 2WD mode, the 4x4 module (PCM) supplies a ground path to the IWE solenoid to apply vacuum to the integrated wheel ends (disengaging the front hubs from the front halfshafts). In 4WD mode, the 4x4 module (PCM) does not supply the ground path to the IWE solenoid, vacuum is not applied to the integrated wheel ends and an internal spring keeps the front hubs engaged to the front halfshafts.
You need to check for vacuum supply at the front hubs when 4x4 is engaged
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