As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED DURING TAKEOFF WE RECEIVED A E2 FIREDET FAIL MESSAGE THEN IT WENT AWAY. THE MESSAGE CAME BACK LATER AND WE RAN THE QRH AND THEN THE MESSAGE REMAINED UNTIL WE WERE SHORT FINAL AND TURNED THE APU FOR A RETURN TO BASE. MX TROUBLESHOT TO BAD ENGINE WIRE HARNESS W407. R & R WIRE HARNESS, OPS TESTED GOOD.