As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD - CREW REPORTED GEAR DOOR OPEN LIGHT ILUMINATED WITH GEAR RETRACTED. EMERGENCY DECLARED FLIGHT LANDED ORD WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. REPLACED LEFT MAIN LANDING GEAR DOOR SENSOR TARGET THAT WAS FOUND TO BE BROKEN. SYSTEM GROUND CHECK NORMAL OPERATION.