As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PDX - AFTER TAKEOFF ON FLIGHT 2527, THE APU FAULT CAUTION ILLUMINATED ALONG WITH AUTO SHUTDOWN OF THE APU. DUE TO ONE IDG ALREADY BEING ON MEL, RETURNED TO THE FIELD AND ACCOMPLISHED A UNEVENTFUL LANDING. MAINTENANCE REPLACED THE APU FUEL FILTER. OPERATIONAL CHECKS GOOD. AIRCRAFT RETURNED TO SERVICE.