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 1HR IN FLIGHT PERFORMED ENG/APU FIRE DETECTION CONTROL MODULE BITE PER FIM 26-10 TASK 801, FOUND FAULT IN APU LOWER DETECTOR FAULT. REPLACED APU OVERHEAT DETECTOR ELEMENT PER AMM 26-15-01, ALL TESTS PASSED, NO FAULTS FOUND.