As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FOR FLIGHT 3864 ON APU RESTART THE CREW REPORTED SMOKE IN THE AFT CABIN. THE AIRCRAFT CAME FROM THE DE-ICE PAD. THE AIRCRAFT WAS REMOVED FROM SERVICE. PERFORMED OPERATIONAL CHECK OF APU. ALL PARAMETERS NORMAL. RAN APU AND PACK FOR 1 HOUR; ALL EVIDENCE OF SMOKE AND ODOR DISSIPATED. SUSPECT DE-ICE FLUID IN APU INLET. OK FOR SERVICE. THE AIRCRAFT WAS RETURNED TO SERVICE.