As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE CREW ABORTED TAKEOFF WHEN THE EFIS COMP MON CAUTION MESSAGE ILLUMINATED AND BOTH HEADING INDICATORS RED FLAGGED. THE AIRCRAFT RETURNED TO THE GATE WHERE MAINTENANCE CYCLED THE AHARS SYSTEM POWER. THE SYSTEM OPERATIONALLY CHECKED GOOD. THE AIRCRAFT WAS RELEASED FOR SERVICE.