Hundreds of Routemaster buses were recalled last month after experts found that rear doors on the vehicles could open while the bus is moving.
423 of the buses were taken off the streets after the Driver and Vehicle Standards Agency raised concerns over the fault in December.
A Transport for London spokesman told City A.M. the recall was launched after a November incident in which one customer was “slightly hurt”. Almost half of the recalled buses have now returned to service.
Gareth Powell, TfL’s director of strategy and contracted services, 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 Transport for London."
The buses were introduced under previous London mayor Boris Johnson, but have proved controversial, with a similar number of the Routemasters recalled in March over a fault with their steering.
The vehicles were a key election promise for Johnson, and introduced to replace the scrapped bendy buses.
However, they have since proved controversial, with many revealed to be running on diesel, rather than a hybrid system which had been claimed to be more environmentally friendly, while a large number also had to be retrofitted with opening windows over concerns linked to the temperatures on board.
Sadiq Khan has said that London will not purchase any more of the vehicles, vowing instead to replace them with a fleet of new Hydrogen buses.
Labour London Assembly member Florence Eshalomi is planning on raising the recall with City Hall chiefs at a local transport committee hearing later this week, and today blasted Johnson's "vanity project".
"Just when you think it can't get any worse for the Routemasters here we have yet another example of the previous Mayor's vanity project costing Londoners dear," she said.
"An 'eco-friendly' bus that ended up running on diesel, and a 'hop on hop off' service that was too expensive to manage. Sauna like conditions in the summer that led to windows being replaced, and now rear doors that can open without warning when the bus is moving. This really is beyond farcical."