Accounting errors led to the wrong figures for net income from continuing operations, which were overstated by about 25 to 35 percent, the world's largest auto maker said in a filing with the Securities and Exchange Commission.
GM has been conducting an internal review of credits received from suppliers and its accounting treatment of them from 2000 to 2005. "This issue is one of the matters that is also being investigated by the SEC," GM said.
GM said the review shows that the auto maker erroneously recognised some supplier credits as income in the year in which they were received rather than in the future periods to which they were attributable.
The car maker said it expects its restatement of financial statements for 2001 to have a material impact to the results previously reported for that year.
GM, which has lost about $3 billion this year, is grappling with high health care costs, foreign competitors cutting into its market share and stalled sales of its profitable sport utility vehicles amid rising gasoline prices.
GM's main parts supplier - Delphi Corp - filed for bankruptcy in October, and GM could face up to $12 billion in liabilities at Delphi.
GM shares earlier in the day fell to their lowest point in 13 years amid increasing concerns the auto maker has underfunded its pension plans and that workers at Delphi could go on strike.
GM in its filing also said it will restate financial statements for periods after 2001 that may be affected by the erroneous accounting.
"However, the effect of any such restatement in subsequent periods is expected to be immaterial to those financial statements," the company said. GM said in its filing on Wednesday that it restated its second-quarter 2005 results to reflect the appropriate value of its investment in Fuji Heavy Industries Ltd GM had said in October that it would make the restatement.