The aircraft still had the majority of its fuel so it was heavier than normal when it landed, causing the brakes to overheat.
The plane had suffered a complete breakdown of the on-board communication system, a problem described as extremely rare, which forced the pilot to communicate via a satellite phone instead.
Merkel, who had planned bilateral meetings with the presidents of the United States, China, Russia and India, was unlikely to arrive in Buenos Aires until Friday evening, German government sources said. Later, Merkel would say she thought something bad had happened in Germany.
Senate defies Trump, showing anger with Saudis for Khashoggi
Bob Menendez, the top Democrat on the Foreign Relations panel, said he would switch his vote and support the resolution. Several senators said they were angry about the absence of CIA Director Gina Haspel from the pre-vote briefing.
It remains unclear if the delay would affect the Merkel's schedule at the G20 summit, which starts Friday.
It was met on the tarmac by fire engines, DPA said, adding that the captain told the passengers the plane would have to turn back as a technical problem was disrupting several electrical systems.
After disembarking, Merkel, her husband Joachim Sauer, Finance Minister Scholz and her security officers sat for some time at a desk in the airport restaurant.
In June, problems with the hydraulics system on the same plane forced President Frank-Walter Steinmeier to take an alternative aircraft to Minsk.
"It was a serious malfunction", Merkel told reporters from Bonn, where her delegation was taken to a hotel.
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