As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FLIGHT THE MEDICAL CREW STATED THAT THERE WAS A STRONG SMELL OF FUEL FUMES IN THE CABIN. PILOT DISCUSSED WITH THE CREW AND THEY DECIDED TO RETURN THE AIRCRAFT TO BASE. AFTER EXTENSIVE TROUBLE SHOOTING THE MECHANINC FOUND A FAULTY FUEL FILLER CAP.