As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED, SMOKE COMING FROM A SQUARE DUCT ON THE LEFT ENGINE COWLING ON TAXI OUT. AIRCRAFT RETURNED TO THE GATE. MAINTENANCE INSPECTED THE LEFT ENGINE AND FOUND OIL RESIDUE AROUND THE INLET TO THE HEAT EXCHANGER. NO EVIDENCE OF OIL LEAKS FOUND ON OR AROUND THE LEFT ENGINE.