As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ETOPS SIGNIFICANT SYSTEM - APU AUTO SHUTDOWN AT GATE (PANEL LIGHTS FLICKER HIGH/LOW) FIRE BELL SOUNDED IN TAIL - NO FIRE HANDLE LIGHTS ILLUMINATED. REPLACED K421 RELAY PER FIM 49-11-00 AND WDM 49-61-11. REMOVED AND REPLACED APU GCU PER AMM 24-22-00 DUE TO APU SERIAL LINK FAULT PER FIM 24-20-00. BITE AND OPS CHECK PK. OK FOR SVC.