As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DECLARED AN EMERGENCY AND RETURNED TO THE FIELD FOR A PROXIMITY SYSTEM CAUTION MESSAGE ON EICAS. THE ACFT LANDED NORMALLY. MAINTENANCE REPLACED THE PROXIMITY SYSTEM ELECTRONIC CONTROL UNIT AND PERFORMED A SYSTEMS CHECK FLIGHT. THE ACFT WAS THEN RETURNED TO SERVICE.