As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMBOUT OF FLIGHT 3478, FROM DTW GREEN HYDRAULIC HI TEMP CAME ON FOLLOWED QRH. AIR RETURN TO DTW. MAINTENANCE GROUND RAN PRESSURIZED HYDRAULIC ON GROUND FOR 1 HOUR AND 20 MINUTES AT NO TIME DID THE GREEN HI TEMP LIGHT ILLUMINATE. INSPECTED GREEN SYSTEM, ALSO COULD NOT DUPLICATE DISC AT THIS TIME. AC OK FOR CONTINUED SERVICE.