As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON TAKEOFF THE NR 2 GEN OFF LIGHT ILLUMINATED WITH ASSOCIATED EICAS MSG. UNABLE TO START THE APU. EMER DECLARED & FLIGHT RETURNED WITHOUT FURTHER INCIDENT. THE ACFT WAS GNDED. SEE ALSO AALA 20160306002. R & R APU INLET DOOR ACTUATOR CONNECTOR D502 IAW STANDARD PRACTICE. OPERATIONS CHECKED GOOD REFERENCE 49-15-06.