UPDATED: 7/18/14 4:06 pm ET
WASHINGTON -- New documents reveal General Motors redesigned faulty ignition switches without changing the part number in more than the 2.59 million small cars at the center of its recall crisis.
Some of those additional vehicles underwent an ignition switch redesign as far back as 2004, GM said in a July 16 letter to regulators that was posted online today by the National Highway Traffic Safety Administration.
In some cases, the part number wasn't changed as would be required. It's possible that the old parts remained in circulation and were used to service vehicles, GM said.
The vehicles identified in the filing are among an additional 7.6 million the company flagged on June 30 for ignition-related issues.
CEO Mary Barra, who took over in January, has been making the case that the automaker's corporate culture regarding safety has changed. Barra has been called before Congress four times this year after it was determined the company waited at least a decade to recall millions of vehicles for ignition switches that could be inadvertently shut off when jarred, cutting power to the engine and deactivating air bags.
The ignition-switch recall began in February with about 2.59 million cars, including the Chevrolet Cobalt, and has since been expanded to cover at least 10 million vehicles.
As far back as 2003, GM received a complaint of a stalling Pontiac Grand Am and engineering changes were ultimately made to increase the turning force required in the ignition switch for that car, according to the letter.
Similar action was taken for some Chevrolet Malibu and Oldsmobile Alero models, the letter shows.
While the part number was changed in those cases, the old part number was designated as "use," making it possible that the faulty switch was used to fix other vehicles, GM said.
In 2004, an engineering change was made to the Pontiac Grand Prix ignition switch to be consistent with the Malibu and Alero changes. GM didn't change the Grand Prix ignition switch's part number.