As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FAULT IN THE NR 1 B LOOP. ACFT GROUNDED. CONFIRMED FAULT, NR 1 ENGINE B LOOP WILL NOT TEST. ENGINE, APU FIRE & OVHT DETECTION CONTROL MODULE BITE SHOWS UPPER FAN LOOP DEFECTIVE. ACCOMPLISHED DETECTOR LOOP RESISTANCE TEST IAW AMM 26-11-00-730-801, CONFIRMED UPPER FAN DETECTOR DEFECTIVE. REMOVED & REPLACED THE UPPER FAN FIRE DETECTOR ASSY IAW AMM 26-11-01, OPS CHECKED NORMAL.