As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
A FLIGHT WAS CANCELLED DUE TO THE OXYGEN LEVEL BEING LOW. THE MAINTENANCE TEAM TROUBLESHOT AND DETERMINED THAT THE OXYGEN CONTROLLER WAS DEFECTIVE. AN OVERHAULED UNIT WAS INSTALLED. THE OXYGEN BOTTLE WAS RESERVICED AND FUNCTIONAL CHECKS WERE SATISFACTORY. THE AIRCRAFT WAS RETURNED TO SERVICE.