As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PDX - AFTER ENGINE START, THE APU FAULT CAUTION ILLUMINATED FOLLOWED BY A APU SHUTDOWN. COMPLIED WITH CHECKLIST AND MESSAGE WENT AWAY. MAINTENANCE FOUND A UNDERSPEED FAULT AND ECU BUSS FAULT IN THE MDC. RESEATED AND CLEANED THE ECU PINS. OPERATIONAL CHECKS GOOD AIRCRAFT RETURNED TO SERVICE. NO PARTS REPLACED.