As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FIRE/OVERHEAT TEST FOR APU START, NR 2 ENGINE LOOP B INDICATOR FAULTS. WHEN IN A TEST, OPERATES NORMALLY. ACFT GROUNDED. REPLACED UPPER FAN FIRE DETECTOR ASSY IAW AMM 26-11-01-000-802 AND 26-11-01-400-802. ETOPS GROUND VERIFICATION TEST PASSED.