As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PSP - CREW REPORTED SMOKE IN THE CABIN. EMERGENCY DECLARED FLIGHT RETURNED PSS LANDED WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. FOUND AUXILIARY POWER UNIT OIL COOLER CRACKED AT CORNER SEAM. REPLACED APU. SYSTEM GROUND CHECK NORMAL OPERATION.