As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PHL - FLT 1073 EN ROUTE PHL TO SJU. THE CREW RECEIVED AN AIR/GND DISAGREE EICAS MESSAGE IN FLIGHT. WHILE RETURNING TO PHL, THE FLIGHT HELD FOR ABOUT AN HOUR TO BURN FUEL TO BRING THE AIRCRAFT UNDER THE MAXIMUM LANDING WEIGHT. AFTERWARDS, THE FLIGHT DECLARED AN EMERGENCY, BUT LANDED IN PHL WITHOUT FURTHER INCIDENT. MAINTENANCE REPLACED THE S246 SENSOR DUE TO LOW INSULATION RESISTANCE.