As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB OUT, A CARGO FIRE SYSTEM FAIL INDICATION OCCURRED. FLIGHT RETURNING TO DEPARTURE. EMERGENCY DECLARED. MESSAGE EXTINGUISHED ON TOUCHDOWN. COMPLIED WITH FIM TASK 26-23-00-810-803-A, NO FAULTS NOTED MESSAGE REMAINS CLEAR. TRANSITORY CONDITION OF THE GENERIC I/O MOD 3, ACFT OK FOR SERVICE.