As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING DESCENT INTO DTW, THE NR 3 ENGINE FIRE WARNING SOUNDED, SHUTDOWN ENGINE AND DISCHARGED BOTH FIRE BOTTLES. POST FLIGHT INSPECTION REVEALED NO SIGNS OF FIRE. TROUBLESHOOTING FOUND THE DUAL FIRE DETECTION CONTROL BOX AT FAULT, REPLACED CONTROL BOX AND BOTH FIRE BOTTLES PER DC-10 MM 26-11-01 AND 26-21-01.