As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: AIRCRAFT RETURNED TO YYZ DUE TO COCKPIT VENTILATON MALFUNCTION AND SENT FUMES AND SMOKE INTO THE COCKPIT. AN EMERGENCY WA DECLARED AND THE AIRCRAFT LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE SWITCHED BLOWER FAN TO OVERRIDE. ACCOMPLISHED MCM CARD 05-96-70. FOUND BLOWER FAN TO CAUSE FUMES. REPLACED BLOWER FAN PER AMM 21-26-51.