As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AIRCRAFT WAS TAXIING FOR DEPARTURE, SMOKE WAS NOTED IN THE CABIN. AN EMERGENCY WAS DECLARED AND ARFF ATTENDED THE ACFT. THE AIRCRAFT WAS CLEARED BY ARFF AND RETURNED TO THE GATE. IT WAS FOUND THAT THE RT AIR CONDITIONING HAD OVER HEATED, CAUSING SMOKE.