As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU AIR ON AT GATE HAZE AND SMOKE IN AFT OF CABIN. BOTH DUCTS WENT UP TO 150 ON THE GROUND. C/W WK'S 2120-2001 & 2120-2002(936244) C/W NO GO ODI PREVENTION 2172. ALSO RMVD INLET DOOR VERIFIED NO CONTAMINATION. CLEANED AS PRECAUTION. VERIFIED NO CONTAMINATION IN CROSSOVER DUCT. C/W FULL DUCT BURNOUT PER AMM 21-53-00-720-801. (LP 4140179)