As General Motors Company (NYSE:GM) prepares to return to the S&P 500 index on Thursday, the U.S. Treasury Department announced it would sell 30 million of its GM shares as part of a 12-to-15-month plan to fully divest from the company it had to bail out amid the 2009 peak of the auto industry crisis.

Treasury’s sale of its GM common stock is part of its continuing efforts to wind down the Troubled Asset Relief Program. To date, Treasury has already recovered nearly 95 percent ($398.15 billion) of the funds disbursed through TARP ($419.97 billion),” the department said in a statement on Wednesday.

The United Auto Workers Retiree Medical Benefits Trust will also sell 20 million shares, the Treasury said.

In November 2010, GM’s initial public offering yielded $13.5 billion to U.S. taxpayers and reduced their stake in the company to 500.1 million shares. In December, GM bought 200 million shares back from the Treasury at $27.50 each.

In January, the Treasury began a 12-to-15-month process of divesting the remaining 300.1 million shares by selling 58.4 million shares to GM for $1.6 billion.

As of April 30, the U.S. government had recovered $30.7 billion of the $49.5 billion it provided to GM in 2009 to stabilize the company during the auto industry crisis. This means GM still owes U.S. taxpayers $18.8 billion of the principal it received because the company was considered too big to fail. The Treasury plans to completely wind down its investment in GM by early 2014.

For more about TARP, read the U.S. Treasury’s latest report to Congress here.