As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DFW - CREW REPORTED AUXILIARY POWER UNIT AUTO SHUT DOWN IN FLIGHT WITH LEFT ENGINE CONSTANT SPEED DRIVE ON PLACARD. FLIGHT RETURNED DFW LANDED WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. REPLACED AUXILIARY POWER UNIT. SYSTEM GROUND CHECK NORMAL OPERATION.