General Motors Co. CEO Ed Whitacre said Thursday he's stepping down Sept. 1.

Whitacre will be replaced by GM board member Daniel Akerson, the managing director and head of global buyout of The Carlyle Group.

Akerson, 61, will be GM's fourth CEO in 18 months when he takes over the job.

Whitacre, 68, was named GM's chairman last July when GM emerged from bankruptcy protection. After he ousted CEO Fritz Henderson, Whitacre was named interim CEO in December and became permanent CEO in January.

Whitacre, the former head of AT&T, often said in a folksy Texas drawl that he knew little about cars. But he shook up the company with a number of managerial changes, including luring Chief Financial Officer Chris Liddell from Microsoft Corp. He also combined sales and marketing responsibilities and consolidated control of GM's core North American market under one executive.

Whitacre said the board was aware of his plans the day he accepted the CEO job, and he predicted a smooth transition.

"I believe we've accomplished what we set out to do," Whitacre said. GM reported its second straight quarterly profit on Thursday.

Akerson has been involved in GM's transition every step of the way, Whitacre said. "He's absolutely the right choice."

Like Whitacre, Akerson has a background in telecommunications. He served in top executive positions at MCI Communications in the 1980s and 1990s.

Whitacre also serves as GM's chairman. He will leave that job by the end of the year.