As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED, RECEIVED AN ENGINE 2 FIRE DETECTION FAIL MESSAGE AFTER TAKEOFF. THE CREW RETURNED TO KORD AND LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED THE ENGINE 2 FIRE DETECTOR. OPERATIONAL CHECKS WERE GOOD WITH NO FURTHER DEFECTS NOTED.