WHy is my Z71 giving me a notice about servicing 4 wheel drive? on 2004 Chevrolet Tahoe

Driving home this afternoon my Tahoe Z71 threw a code and a message told me service 4WD there were no sounds from underneath or anywhere else . Just wondering what the issue could and how much the approximate cost on the part would be? What I think it may be is the sensor went bad. Just let me know if this even remotely sound s right. Thanks, Julian

Asked by for the 2004 Chevrolet Tahoe