As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF IN KSTL, THE AIRCRAFT HAD A LANDING GEAR AIR GND FAIL MSG ON EICAS. THE CREW RETURNED THE AIRCRAFT TO KSTL FOR AN UNSCHEDULED LANDING. MAINTENANCE INSPECTED AND FOUND THE RIGHT MLG WOW PROX SWITCH OUT OF ADJUSTMENT. MAINTENANCE ADJUSTED WOW PROX SWITCH AND OPS CHECK GOOD.