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 DIVERTED TO COS DUE TO A YELLOW HYDRAULIC SYSTEM RESERVOIR LOW LEVEL MESSAGE AFTER TAKEOFF. THE AIRCRAFT LANDED SAFELY AT COS WITHOUT FURTHER INCIDENT. MAINTENANCE REPLACED THE YELLOW HYDRAULIC SYSTEM RESERVOIR LOW LEVEL SWITCH PER AMM 29-13-41 AND ACCOMPLISHED A SATISFACTORY OPERATIONAL CHECK.