As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PDX- SMOKE DETECTOR IN LAVATORY SOUNDING, WITH SLIGHT OIL SMELL IN AFT CABIN. APU STARTED APPROXIMITLY 15-20 MINUTES WITH CABIN HEATING SELECTED ON. ALARM STOPPED ABOUT ONE MINUTE AFTER SELECTING THE APU AIR OFF.REMOVED AND REPLACED APU. OPERATIONAL CHECKS GOOD. AIRCRAFT RETURNED TO SERVICE.