As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NR 1 ENGINE FIRE DETECTION LOOP B FAULT. ACFT GROUNDED. PERFORMED ENGINE & APU FIRE DETECTION CONTROL MODULE BITE IAW FIM 26-10 TASK 801. FOUND HARD FAULT FOR THE NR 1 ENGINE UPPER FAN DETECTOR FAULT. REMOVED AND INSTALLED NEW M1760 IAW AMM 26-11-01. PERFORMED ENGINE FIRE DETECTION OPS TEST IAW AMM 26-11-00. SYSTEM CHECKED NORMAL.