As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT FLYING LEVEL AT 12,000 FT WHEN FLIGHT CREW NOTICED STRONG ODOR IN COCKPIT. CREW RETURNED TO DEPARTURE AIRPORT WITHOUT INCIDENT. MAINTENANCE TROUBLESHOOTING REVEALED THE FORWARD VENT BLOWER WAS DEFECTIVE, MAKING GRINDING NOISE AND THE CAUSE OF THE REPORTED ODOR. MAINTENANCE REPLACED DEFECTIVE VENT BLOWER AND RETURNED THE AIRCRAFT TO SERVICE.