As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT RETURNED TO EWR UNDER AMBER ALERT DUE TO CENTER HYDRAULIC QUANTITY EICAS MESSAGE. *S/D* THE C HYD QTY EICAS MESSAGE APPEARED AND QUANTITY SHOWED .38. SYSTEM AND PUMP LOW PRESSURE LIGHTS DID NOT COME ON. HYD QUANTITY WAS VERIFIED FULL AFTER LANDING. PIN NR 3 ON CENTER QUANTITY TRANSMITTER WAS FOUND PUSHED BACK. TRANSMITTER REPLACED.