As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI-OUT CREW REPORTED ODOR AND HAZE IN THE CABIN AND RETURNED TO THE DEPARTURE GATE. MAINTENANCE FOUND A HYDRAULIC LEAK AT THE LEFT ENGINE FILTER MODULE PRESSURE LINE FITTING. THE FITTING O-RING WAS REMOVED AND REPLACED AND A GOOD LEAK CHECK ACCOMPLISHED. COMPLETED MINI DUCT BURNOUT AND DEFERRED THE APU FOR CLEANING.