As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER ENGINE START WITH APU OFF, FUMES & SMOKE COULD BE SEEN & SMELLED IN THE CABIN. PERFORMED TROUBLESHOOTING IAW MM 21-52-00 & FOUND ODOR TO BE COMING FROM COCKPIT ACM. R & R THE AFT ACM TURBINE WITH A NEW AIR BEARING ACM TURBINE. PERFORMED OPERATIONAL TEST WITH NO FURTHER DEFECTS FOUND IAW AMM 21-00-00 & COMPLIED WITH SERVICE LETTER SL750-21-02R4.