What was found
FT # 1011, BOS-ORD. RETURNED TO FIELD. DURING FLT STRONG ODOR OF EXHAUST IN COCKPIT AND FWD PORTION OF GALLEY AND CABIN; REF TROUBLESHOOTING TAB FOR WORK PERFORMED FOR THIS DEFECT ITEM. RAN BLEEDS WITH APU FOR 40 MINUTES WITH NO ODOR. THEN WITH #1 ENG , NO ODOR. #2 BLEED ON MEL. CABIN FILTERS REPLACED IAW AMM 21-42-02. REF AMM 21-24-02, 21-51-00, 71-00-01. MCC REQUESTED CLEARING MDDR 406203 TAT #2. R & R TAT #2 PROBE, SEE DEFECT 2642184 ITEM #2. AIRCRAFT OK FOR SERVICE. AMM REFERENCES 21-24-02, 21-51-00, 71-00-01.