As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLYING CMH - EWR, CREW REPORTED THAT THE LANDING GEAR WOULD NOT RETRACT. AN EMERGENCY WAS DECLARED AND CREW RETURNED TO CMH WHERE THEY LANDED WITHOUT INCIDENT. MAINTENANCE TROUBLESHOT, REMOVED AND REPLACED PROX SENSOR HARNESS AND ADJUSTED PROX SENSOR 1 PER AMM AND OPS CHECKED GOOD.