As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SEA - AIRCRAFT RETURNED TO FIELD WHEN PITCH TRIM CAUTION ILLUMINATED, AND AUTO TRIM FAIL MESSAGE APPEARED. NO TRIM WAS AVAILABLE TO EITHER SIDE AND AUTO PILOT WOULD NOT ENGAGE. TRIM INDICATOR DISPLAYED FULL NOSE UP. MAINTENANCE INSPECTED THE AIRCRAFT AND COMPLIED WITH THE SERVICE INFORMATION LETTER DHC8-400-SL-27-003 PROCEDURE. NO DEFECTS WERE NOTED, NO PARTS REPLACED, AND OPERATIONAL CHECK WAS OK. AIRCRAFT RETURNED TO SERVICE.