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 ORD DUE TO THE FLIGHT CREW REPORTING YELLOW HYDRAULIC RESERVOIR OVERHEAT, YELLOW ENGINE 2 PUMP LOW PRESSURE AT 1500 AGL - THE AIRCRAFT LANDED SAFELY AT ORD AND WAS TOEED TO THE GATE - MAINTENANCE REPLACED THE YELLOW ELECTRIC PUMP CHECK VALVE AND ACCOMPLISHED A SATISFACTORY OPERATIONAL CHECK PER AMM 29-24-21