As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
TAXIED OUT ON LEFT ENGINE. STARTED 2ND ENGINE. CAPTAIN SMELLED SMOKE. RETURNED TO GATE. BOTH ENG BLEED OFF. ALSO ISOLATED PACKS AND RECIR, NO SMELL OR SMOKE NOTED. ALL LIGHTS IN CABIN ON VIDEO ON, CHECKED ALL CARGO PITS AND E&E COMPARTMENT, NO SOURCES SMOKE OR SMELL. CAUSE OF SMELL NOT ESTABLISHED.