As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FUMES IN COCKPIT DURING TAXI ,STARTED WITH APU BLEED FIRST AND THEN WITH ENGINE BLEED. TRIED TO ISOLATE PACKS. ODOR CONTINUED. RETURNED TO GATE. THE APU OIL CAP WAS FOUND OFF BY MAINTENANCE, INSPECTED AND RAN APU ON GROUND WITH NO ODORS FOUND APU PROPERLY SERVICED.