As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT 172 NRT-JFK RETURNED TO NRT WITH THE NR 1 ENGINE SHUTDOWN BY THE CREW DUE TO A FIRE WARNING. MAINTENANCE FOUND A BROKEN DETECTOR ELEMENT. THE ELEMENT AND TWO DETECTOR CARDS WERE REPLACED. RAN NR 1 ENGINE AND THE ENGINE FIRE DETECTION SYSTEM TESTED NORMAL.