General Motors CEO Mary Barra tells U.S. lawmakers today the automaker’s response to ignition-switch complaints dating back more than decade is disturbing and unacceptable, but no longer characteristic of how the company now operates.

Barra’s testimony before the House Committee on Energy and Commerce Subcommittee on Oversight and Investigations comes on the same day the automaker reports an 8.1% increase in March deliveries, the first full month of sales under the shadow of an ignition-switch recall linked to 13 deaths and 31 crashes.

GM sold 256,047 vehicles last month, compared with 245,950 in the same period last year, according to WardsAuto data. There was one fewer selling day than in March 2013.

GM small-car sales last month appeared to have held up against the highly publicized recall, which covers similarly sized vehicles although those models are no longer in production.

Sales of the Chevrolet Cruze, which in 2010 replaced the Chevy Cobalt at the center of the recall as GM’s C-segment offering, rose 15.5% to 26,521 units. Sales of the smaller Sonic B-segment car, which GM did not sell when it produced the faulty switch, increased 51.2% to 10,060.

A WardsAuto examination of sales data at the height of the 2010 Toyota sticky-accelerator pedal recall and the 2000 Ford-Firestone recall showed little evidence of long-term sales damage.

Barra, who was scheduled to be joined on Capitol Hill by NHTSA Acting Administrator David Friedman to answer why the government’s safety watchdog missed signs of the defective part in investigations during the mid-2000s, spent much of her testimony telling lawmakers an internal investigation by GM would provide answers behind the slow-moving recall.

Documents show GM knew as far back as 2003 about a problem with ignition switches that can unintentionally move out of the “run” position to “off” or “accessory” and disable the engine and electronics such as the power steering and airbags, but a recall did not come until Jan. 31, 2014. GM expanded the recall in February to 2.2 million vehicles in the U.S. and 2.6 million gloablly.

“I want to know that answer as much as you,” Barra tells the lawmakers, reiterating several times the automaker has hired Anton Valukas, chairman of the law firm Jenner & Block, to investigate what went wrong.

Barra also calls it “unacceptable” that GM redesigned the ignition switch in 2006 but did not change the part number. Changing the part number would have allowed the automaker to more effectively track its installations.

However, it also leaves GM open to allegations of a cover-up, as Rep. Marsha Blackburn (R-TN) suggests in her questioning of Barra.

“That is the question I’ve asked Mr. Valukas to uncover,” Barra tells Blackburn. “And I am anxiously awaiting the results from his study.”

Also central to lawmakers’ questions: why GM would accept a part that did not meet its internal specifications. Barra draws a parallel to the purchasing of steel, where GM sets a specification for the material but due to the number of suppliers it sources from and varying degrees of availability the automaker could lower its expectations.

“You’ll assess the performance, the functionality, the durability, the aspect of the part or (material) to live up to what the performance, durability and safety needs to be,” she says.

Pressed by Subcommittee Chairman Rep. Tim Murphy (R-PA) if she considers the ignition switch acceptable, Barra replied, “As we clearly know today it is not.”

Asked if GM in the future would buy parts that did not meet specifications, Barra tells lawmakers, “We will not accept parts that do not meet our performance, safety, durability (and) functionality requirements.”

Barra also says the automaker will hold individual employees accountable for actions taken while the ignition switch was in production, and reveals GM has hired victims’ compensation expert Kenneth Feinberg as a consultant.

GM says Feinberg, who handled compensation issues related to 9/11, the BP oil spill in the Gulf of Mexico and the Boston Marathon bombing, will “explore and evaluate options in its response to families of accident victims whose vehicles are being recalled for possible ignition-switch defects.”

Barra testifies tomorrow before a Senate panel.