As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
JUST AFTER TAKEOFF THE CREW RECEIVED A LANDING GEAR AIR/GROUND FAIL MESSAGE. THE FLIGHT RETURNED TO THE FIELD WITHOUT INCIDENT. MAINTENANCE FOUND THE LT AFT PROXIMITY SWITCH TARGET OUT OF ADJUSTMENT. PROCEEDED TO REPLACE THE SWITCH AND CORRECT THE ADJUSTMENT. ALL OPERATIONAL CHECKS ARE GOOD AT THIS TIME.