As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RETURNED TO FIELD DUE TO A VERY STRONG TOXIC ODOR DURING CLIMB THROUGH 4000 FT, STRONG BY 8-9000 FT. FRONT OF CABIN AND COCKPIT. DETERMINED CAUSE TO BE ONE OF THE ENGINES. ACCOMPLISHED ECS DECONTAMINATION IAW 21-00-00-615-003-A. R & R THE RECIRCULATION FILTERS 1 & 2 AS A PRECAUTION. PERFORMED VISUAL INSPECTION OF APU & ASSOC BLEED DUCTS. FOUND NO SIGNS OF OIL CONTAMINATION.