As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) ACFT RETURNED DUE TO DEPRESSURIZATION AND BURNING ODOR IN THE COCKPIT. ATC CALLED LOCAL STANDBY, NO PAN/MAYDAY DECLARED. ACFT LANDED SAFELY AND WITHOUT INCIDENT. MAINT INTEROGATEED THE CDS, THE FOLLOWING CODES IDENTIFIED: AFT OUTFLOW VALVE FAIL CPC/OFF VALVE DATA FAIL. AFT OUTFLOW VALVE REPLACED. FUNCTION CHECKS OF ECS SYSTEM CARRIED OUT COULD NOT IDENTIFY ANY ODORS. AIRCRAFT RETURNED TO SERVICE.