As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE FLIGHT CREW RECEIVED A LANDING GEAR AIR/GROUND FAIL MESSAGE IMMEDIATELY AFTER TAKEOFF, AND THE GEAR WOULD NOT RETRACT. THE ACFT RETURNED TO DEPARTURE AND LANDED WITHOUT INCIDENT. THE ACFT WAS FERRIED WITH THE GEAR EXTENDED FOR FURTHER TROUBLESHOOTING. ALL 3 LANDING GEAR STRUTS WERE FULLY SERVICED WITH FLUID AND NITROGEN. RELAYS K0453, K0753, AND K0325 WERE REPLACED AS WELL.