General Motors on Wednesday said it has shipped “thousands” of kits needed to repair the defective ignition switches linked to at least 13 deaths.

The No. 1 U.S. automaker also said letters were mailed last week to about 1.4 million owners of 2003-2007 models alerting them to contact dealers to schedule repair appointments, which should take about 90 minutes. Dealers have already reported receiving the parts and making repairs.

Without warning, the current switches can make vehicle engines stall while operating, stop airbags from deploying, and power steering and power brakes from operating. GM is under investigation by U.S. safety regulators, Congress and the U.S. Department of Justice for why it did not catch the faulty part for over a decade.

GM said on Wednesday that owners of 2008-2011 models subject to the recall, which has affected 2.6 million vehicles, will receive a letter in early May confirming their inclusion in the recall. Another letter alerting them when replacement parts are available will follow.

The Detroit company did not provide a more detailed number of how many of the parts have been shipped, but said the kits include ignition switches, ignition cylinders and key sets.

GM had previously asked its switch supplier, Delphi Automotive, to double production at its Mexican plant, as well as add a third line to speed production of the replacement parts. GM has said it may not complete the repairs until around October.