As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
EXECUTED A GATE RETURN WITH AN ODOR IN THE CABIN. TROUBLE SHOT IAW FIM 21-00-01/301. INSPECTED INLET OF LT AND RT PACKS FOR FLUID INGESTION. NONE FOUND, NO EVIDENCE OF FLUID AROUND APU INTAKE. RAN PACKS FOR SEVERAL HOURS, NO ODOR NOTICED. RAN ENGINES WITH PACKS, NO ODOR.