As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LEFT HYDRAULIC SYSTEM LOW PRESSURE LIGHT ILLUMINATED AFTER TAKEOFF. CREW PERFORMED COCKPIT OPERATING MANUAL PROCEDURES AND NORMAL PRESSURE WAS ACHIEVED USING ALTERNATE PUMP. FLIGHT RETURNED TO DTW AND LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED LEFT ENGINE DRIVEN HYDRAULIC PUMP, OPERATIONAL CHECK NORMAL.