As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT 7860, IAD TO YOW - EN ROUTE TO CYOW THE FLIGHT CREW RECEIVED AN "AHRS 2 OVERHEAT" MESSAGE ON EICAS. THE QRH WAS FOLLOWED AND DISPATCH WAS CONTACTED ALONG WITH MAINTENANCE CONTROL AND IT WAS DETERMINED THAT RETURNING TO IAD WOULD BE THE BEST COURSE OF ACTION. THE AIRCRAFT RETURNED TO IAD AND LANDED WITHOUT INCIDENT. MAINTENANCE FOUND THE AHRS FAN TO BE INOP. THE FAN AND FILTER WERE REPLACED AND THE AHRS SYSTEM OPS CHECKED GOOD.