As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON CLIMBOUT THE -EFIS COMP MON- CAUTION MESSAGE ILLUMINATED AND THE CAPTAIN'S HEADING WAS 30 DEGREES 60 DEGREES OFF. THE FLIGHT RETURNED TO DAY AND LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED THE NR 1 AHRS ATTITUDE/HEADING COMPUTER WITH A SERVICEABLE UNIT. THE SYSTEM OPERATIONALLY CHECKED GOOD. THE AIRCRAFT WAS RELEASED FOR SERVICE.