Growth is brisk but slower than expected, causing automakers to question their multibillion-dollar investments in new factories and raising doubts about the effectiveness of federal incentives.
The company, a General Motors subsidiary, has hired a law firm to investigate how it responded to regulators, as its cars sit idle and questions grow about its C.E.O.’s expansion plans.
General Motors became the last of the three large U.S. automakers to reach a tentative agreement on a new contract with the United Automobile Workers union.