Ballymena firm Wrightbus is carrying out an update on its London Routemaster buses after a software glitch caused a problem with its doors.
More than 400 Routemasters - known as the Boris Bus - are to be brought back to garages in the city after a passenger was injured in November.
Transport for London (TfL) said it informed the Department for Transport and Driver & Vehicle Standards Agency and the decision was made for the buses to be brought back for software updates.
The malfunction happened when a driver repeatedly pressed the 'door close' button.
The system became overloaded with close requests, causing a rear door to open.
Because the bus is programmed to brake when the doors open at speeds below 5mph, it braked suddenly, causing the injury to a passenger.
Wrightbus said it would not comment on the issue.
TfL said it was not footing the bill for the issue to be fixed.
Gareth Powell, a director at TfL, said: "The fault we identified would only occur at very low speed and if the driver doesn't follow the correct procedure. As a precaution, the manufacturer, Wrightbus, is carrying out a software update at no cost to TfL."
More than half the affected buses have already been updated, with the work to be completed as soon as possible.
So far TfL has spent £350m on 1,000 of the hybrid buses, which cost £350,000 each.
But London Mayor Sadiq Khan, who succeeded Boris Johnson last year, has warned no more of the buses will be purchased by TfL, as he wishes to introduce more environmentally-friendly vehicles.
However, it's thought the Routemaster could be replaced with other buses made by Wrightbus.
Last year nearly 500 of the Routemaster vehicles were recalled because of steering problems.