As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IN CRUISE FLIGHT APU DET INOP CAME ON WITH ASSOCIATED MASTER CAUTION. IT WOULD LIGHT UP EVERY FEW SECONDS FOR A FEW SECONDS GO OUT THEN REPEAT, APU HAS NOT BEEN ON. ACCOMPLISHED APU FIRE DETECTION OPERATIONAL TEST AND ENG/APU FIRE DETECTION CONT MODULE (M279), BITE OPS NORMAL REF MM 26 15 00 710 801. REMOVED AND REPLACED ENG AND APU FIRE DETECTION MODULE, OPS NORMAL. REF MM 26 10 01 400 801 MM 26 11 00 710 801 AND MM 26 15 00 710 801.