As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER PUSH BACK GROUND CREW SAW SMOKE FROM UNDERNEATH AIRCRAFT. 30 SECONDS LATER PAC 1 FAIL MESSAGE APPEARED. PERFORMED PAC 1 FAIL RE-SET ACCORDING TO 2.6 OF THE QRH. AFTER 10 SECONDS OF COMPLETING QRH 2.6 PAC 1 FAIL MSG APPEARED AGAIN. PLACED ON MEL 21-51-00A. RETURNED TO SERVICE. PERFORMED ODOR/SMELL CHECKLIST WITH NO DEFECTS NOTED. CHECKED WIRING NO DAMAGES FOUND. FAULT CODE 21515700AM1 AIR CYCLE MACHINE.