As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD - CREW REPORTED "LEADING EDGE SLAT ASYMMETRY" EICAS MESSAGE JUST AFTER TAKEOFF. EMERGENCY DECLARED FLIGHT RETURNED ORD LANDED WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. FOUND SENSOR 303 ON NUMBER 9 SLAT FAULTED. REPLACED SENSOR. SYSTEM GROUND CHECK NORMAL OPERATION.