As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RECEIVED LEVEL 2 TANK WING OVERFILL WARNING INFLIGHT. SINCE NR 3 TANK QTY WAS INSP, HAD NO WAY OF VERIFYING IF FUEL WAS VENTING OVERBOARD. DECLARED EMERGENCY AND RETURNED TO DEPARTURE. FOUND 6 GALLONS FUEL IN RT VENT BOX. DRAINED OK. TROUBLESHOT IAW FIM 28-14-2-00, NO FAULT FOUND. REPLACED TANK-1 FILL VALVE CONTROLLER AS A PRECAUTION IAW AMM 28-21-02. ACFT OK FOR SERVICE.