As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU AUTO SHUTDOWN AT GATE. FOUND APU COOLING FAN-OIL COOLING AIR DISCHARGE, TO BE REVERSE FLOW. THIS SHOULD BE AN EXHAUST, INSTEAD IS ACTING AS AN INTAKE. SUSPECT FAN IS RUNNING IN REVERSE. REMOVED FAN. FOUND APU GEARBOX DRIVE GEAR WITHOUT TEETH. REMOVED APU. COMPLETED INSTALLATION FROM SUB TASK 864-043 TO END.