As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU FIRE WARNING INDICATION. *S/D* TROUBLESHOOTING FOUND APU LOOP M515 READING 234 OHMS TO GROUND. THIS READING WAS OUT OF LIMITS. REPLACED M9323 APU TAILPIPE DETECTION HARNESS, AND TESTED SYSTEM PER AMM 26-15-00, SYSTEM CHECKED NORMAL. ALSO, REPLACED THE APU FIRE BOTTLE, SQUIB AND DISCHARGE DISC INDICATOR.