Kinda sounds like this may be the issue. Would be helpful if you could scan it for the code.
Customers may comment about a Service 4WD light on solid or intermittently. Technicians may discover a C0306 DTC hard set or in history.
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Recommendation/Instructions:
This concern may be caused by high resistance through the motor brushes. The highest concentrations of concerns have occurred in geographic locations with low 4WD usage.
If the DTC C0306 is current or in history dealers should clear the DTC from history then cycle the actuator motor 25 times by shifting the transfer case between 4hi, 4hi lock and 4lo lock. A revised interim software reflash is available in TIS2WEB. This software was released to dealers 07/22/07 on version 7.5. Reflash the TCCM (Transfer Case Control Module) with the latest calibration listed in TIS2WEB.