As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 1203 EWR-SDQ. RETURNED TO FIELD. ELECTRICAL SMELL ABOVE 1000 FT. RAN QRH SMELL PERSISTED TO LANDING. ELECTRICAL ODOR LATER DETERMINED TO BE OILY CABIN ODOR ISOLATED TO PACK 1 WHILE IN OPERATION (PACK-SINGLE (N703 AND UP)(SPEEDBRAKES OK). R & R PACK 1 OZONE FILTER, IAW AMM 21-51-41. OPERATIONS CHECK GOOD, NO SMELL ODOR NOTED. COMPLIED WITH INFOMATION NOTICE 2017-T015F SECTION A CLEARS MDDR MX-4 UPDATED MCC NOTIFED.