As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED FLAPS FAIL AT 20 DEGREES ON APPROACH INTO DCA. CREW DIVERTED TO IAD AND LANDED WITHOUT INCIDENT. MAINTENANCE TROUBLESHOT THE AIRCRAFT, REMOVED AND REPLACED THE FLAP ELECTRONIC CONTROL UNIT (FECU) AND PERFORMED CHECKS USING THE AIRCRAFT MAINTENANCE MANUALS. AIRCRAFT WAS RELEASED FOR SERVICE.