Our 2007 Chevy Tahoe 4 X 4 recently displayed a "Service Four Wheel Drive" panel light a couple of days ago (upon ignition on a sunny, dry day). The light had been steady which, when we read the owners manual, indicates a problem but no immediate service required. One of the possible solutions was to remove and close the gas cap in case it had been incorrectly closed during the last gas-up. That did not work. Yesterday, during a snow storm, I tried using the 4WD. The dial would move to the different settings, but no 4WD activated and no light illuminated indicating which gear it was in (2WD, Auto, 4H, 4L). We checked the fuse for the 4WD but it is OK.