General Motors Co. Chief Executive Mary Barra returns to Capitol Hill this week for what may be her last and toughest hearings with U.S. lawmakers over the auto maker's botched response to a faulty ignition switch that has landed GM in hot water with federal regulators and the Justice Department, reported The Wall Street Journal.

On Thursday, Ms. Barra will face Sen. Richard Blumenthal (D., Conn.), one of her harshest critics, and Sen. Claire McCaskill (D., Mo.), who remains skeptical of GM's response to the issue and its internal probe that cleared the auto maker's executive team and pinned the lack of response on lower-level engineers, lawyers and a dysfunctional company culture. It took the auto maker nearly 11 years to issue a recall for the 2.6 million Chevrolet Cobalt, Saturn Ion and other older model vehicles equipped with the faulty switch.

Ms. Barra needs a smooth hearing process as she looks to move the focus from the Detroit-based auto maker's recall woes and back to the company's strong sales and financial performance. The auto maker is set to release its second-quarter earnings later this month. This will be Ms. Barra's second appearance before a Senate subcommittee.

Most of the attention for the past five months has been on the ignition-switch issue. The defective switch can slip from the "run" to "accessory" position if the key is jarred or bumped. As a result, power can be cut to the vehicle disabling the electronic steering and air bag deployment. GM has attributed 13 deaths to accidents involving the faulty ignition switch, although plaintiff attorneys say the number is much higher. The company has dismissed 15 employees, disciplined five others, revamped some of its internal operations and recalled millions of cars for a variety of issues.

Compensation expert Kenneth Feinberg, hired by GM to handle payouts to victims, will also testify and is expected to be asked for more information on how many people he estimates have been hurt or killed. Mr. Feinberg has declined to provide a figure until he reviews claims. The claim process runs from Aug. 1 through the end of the year.

Chicago attorney Anton Valukas, who handled GM's internal probe, has also been called to testify.

Rounding out the witness list are Michael Millikin, GM's general counsel, and Delphi Automotive PLC CEO Rodney O'Neal. It's the first time either will testify in the matter. As the auto maker's top lawyer, Mr. Millikin is expected to face questions about why he didn't know about the ignition-switch problem sooner since lower-level lawyers were settling Cobalt crash claims out of court.

Mr. O'Neal will be asked how his company interacted with GM in the design and manufacturing of the switch. Delphi contends it was only following GM's direction, including a move by former GM engineer Raymond DeGiorgio, who modified the switch in 2006 but approved keeping the part identification number unchanged. That move, according to GM's internal report, kept the switch issue hidden while sidelining the auto maker's ability to detect the problem sooner.