As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD FLT 5983 THE CREW REPORTED A AIR/GROUND FAIL MESSAGE AFTER TAKEOFF. THE AIRCRAFT RETURNED TO ORD AND LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED AND PERFORMED PROXIMITY SWITCH INSPECTION OF BOTH THE MAIN AND NOSE GEAR. FOUND THE NOSE GEAR WOW PROXIMITY SWITCH CONNECTOR LOOSE AND DIRTY. THE PLUG WAS CLEANED AND RESECURED. OPERATIONAL CHECKS WERE GOOD.