As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU FAILED TO START 3 ATTEMPTS APU DOOR STAT MESSAGE. REPLACED APU CONTROLLER, NO HELP. LEFT NEW CONTROLLER INSTALLED. FOUND 28 VOLTS AT INLET DOOR CONNECTOR, PINS 5, 6. SUSPECT ACTUATOR AT FAULT. MANUAL OPEN APU INLET DOOR FOR TROUBLESHOOTING ATTEMPTED START, UNSUCCESSFUL RE-COLLARED DOOR CIRCUIT BREAK DOOR IN OPEN POSITION. REPLACED INLET DOOR ACTUATOR.