As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED AND THE AIRCRAFT RETURNED TO DFW DUE TO THE FLIGHT ATTENDANTS REPORTING A STRONG ODOR THAT SMELLED LIKE VOMIT AND DIRTY SOCKS AFTER TAKE OFF AND DURING CLIMB. THE AIRCRAFT LANDED SAFELY AT DFW WITHOUT FURTHER INCIDENT. MAINTENANCE ISOLATED THE SOURCE OF THE ODOR TO THE APU AFTER FINDING EVIDENCE OF OIL LEAKS. MAINTENANCE REPLACED APU PER TASK CARD 26L31049003.