Airport spokesman Jeff Green says the trains stopped around 10:20 a.m. November 12 but were running normally within about 50 minutes.
The cause is under investigation but Green says sabotage is not suspected.
Green says some passengers were led off at least one train car and taken back to a concourse. Buses carried some passengers to their concourses during the shutdown.
The underground trains connect the main terminal with the three freestanding concourses. Concourse A can also be reached by an enclosed pedestrian bridge, but Concourses B and C are accessible only by the trains.