As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
"APU DET INOP" LIGHT ILLUMINATED DURING CRUISE FLIGHT. GROUNDED - YES. ENG/APU FIRE DET CTRL MOD SHOWS APU TAIL PIPE LOOP FAULT. REMOVED AND REPLACED APU OVERHEAT DETECTOR ASSY IAW AMM TASK 26-15-01-000-802/26-15-01-400-802. APU FIRE DETECTION OPERATION TEST VERIFIED PER AMM TASK 26-15-00-710-801.