Fritz Henderson had been dubbed Mr. Fixit for his work revamping troubled sectors of General Motors in difficult times. He resigned Tuesday. (Carlos Osorio/Associated Press)

Fritz Henderson resigned Tuesday as chief executive officer of General Motors, less than a year after taking over the position.

The board of the automaker announced its chair, Ed Whitacre, would be Henderson's interim replacement. Henderson had been CEO since March.

The board made the announcement at an afternoon news conference in Detroit.

General Motors says a search for a new CEO will begin immediately. (Paul Sancya/Associated Press)

Whitacre gave no reason for Henderson's resignation, and told journalists the search for a replacement would begin immediately. He took no questions. The chair said the immediate priority for the company is to repay U.S. and Canadian taxpayers as soon as possible.

The Canadian and Ontario governments have given GM's Canadian division $3 billion in loans. The automaker has received $6.7 billion US in U.S. government loans.

Henderson spent the first few months of his term working with the U.S. government to reorganize the automaker outside of bankruptcy, but eventually took the company into Chapter 11 protection in June. With the government's help, the company emerged from court protection in just 40 days cleansed of massive debt and burdensome contracts that would have sunk it without federal loans.

Henderson continued to downsize the automaker after its emergence from bankruptcy. He sought to scale down GM to just four core brands: Chevrolet, Cadillac, Buick and GMC. While he largely succeeded in that goal, attempts to sell the company's other brands hit obstacles.

The company is winding down Pontiac and was successful in winning a tentative sale of Hummer to a Chinese construction machinery maker.

Talks to sell Saturn, Saab fell through

However, Henderson's bid to sell Saturn to racecar mogul Roger Penske fell through and the brand is now liquidating. Last week, Swedish sports car maker Koenigsegg Automotive AB dropped out of a deal to buy Saab. The automaker has said it is talking to "several interested parties" on selling the Saab brand but will phase it out if no deal is reached before the new year.

GM pulled out of a deal to sell its Opel division to Canadian auto-parts maker Magna International last month.

Henderson had been dubbed Mr. Fixit for his work revamping troubled sectors of General Motors in difficult times, and at the time of his appointment was considered an obvious choice to succeed Richard Wagoner.

With files from The Associated Press