As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLYING, CREW RECEIVED AN AFT SERVICE DOOR OPEN INDICATION. CREW DID NOT DECLARE AN EMERGENCY AND ELECTED TO RETURN TO DEPARTURE WHERE THEY LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED, FOUND DOOR OPERATED NORMALLY AND TIGHTENED CONNECTOR PLUG ON PROXIMITY SENSOR IAW AMM AND OPS CHECKED GOOD.