As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD - CREW REPORTED AFTER GEAR WAS EXTENDED YELLOW GEAR DOOR OPEN LIGHT STAYED ON. ACCOMPLISHED GO AROUND AND CHECK LIST AND LIGHT STAYED ON. EMERGENCY DECLARED FLIGHT LANDED ORD WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. FOUND LEFT MAIN GEAR DOOR SENSOR FAULTY. REPLACED D1-30 SENSOR. SYSTEM GROUND CHECK NORMAL OPERATION.