As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU FIRE LOOP 1 STATUS MESSAGE. PERFORMED TROUBLESHOOTING OF THE APU FIRE LOOP 1 IAW FIM 26-15-803. INSULATION RESISTANCE TEST PASSED. RESET AFOLTS CARD M685 SYSTEM FUNCTIONED NORMAL. REMOVED AND REPLACED THE APU FIRE DETECTION CIRCUIT CARD IAW AMM 26-10-01, OPS CHECKED GOOD.