As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ACFT RETURNED TO GATE WITH A SLATS PRIMARY FAIL EICAS MESSAGE. PREVIOUS INBOUND WRITE UP AND THE PRIMARY CONTROL VALVE WAS REPLACED. CLEANED AND RECONNECTED PRIMARY CONTROL VLV CONNECTOR AND ALL SLAT POS SENSORS CONDITION, CHECKED FLAP SLAT OPERATION PER AMM, INDICATION AND OPERATION NORMAL.