NEW YORK (CNNMoney.com) - General Motors Corp. on Tuesday restated nearly four years of results for its GMAC finance unit -- a subsidiary in which it's trying to sell a controlling stake to raise cash and boost its finances.

The company also disclosed that its complex accounting relationships with suppliers are now the subject a criminal probe, in addition to the previously disclosed civil investigation.

Shares of Dow component GM (Research) were down 3 percent in heavy Frankfurt trading Wednesday after falling 1.7 percent in after-hours trading following the latest disclosures by the company.

The restatement was disclosed in after-hours filings with the Securities and Exchange Commission, including its 10-K report for 2005, which details full-year results.

GM's statement warns that the accounting change could affect its ability "to complete a transaction with a strategic investor regarding a controlling interest in GMAC while maintaining a significant stake in GMAC." But that warning came in a long list of possible risks that are generally boilerplate in such financial disclosures.

Realistically, analysts believe that the sale will not be derailed by the accounting disclosures, though the questions certainly don't make GM's negotiations any easier.

"I would have to believe at this point that bidders who are serious players, to the extent they've already done their due diligence, this is not a surprise," auto analyst Kevin Tynan of Argus Research said earlier this month when the GMAC accounting issues were first disclosed. "What it could do is tip the balance more to the buyer, give them a little more leverage on the price."

The company's filing did admit that the restatement was a result of "control deficiency" in its accounting practices, which it conceded "constitutes a material weakness."

The company also disclosed in its filing that a federal grand jury recently issued a subpoena in connection with supplier credits. While the company disclosed last October that the SEC was conducting its own probe of those transactions, this is the first indication that there could be a criminal as well as a civil investigation of those accounting practices being conducted.

GM spokesman Jerry Dubrowski said the company had no further comment on the disclosure of the criminal investigation.

The filing does not detail whether the grand jury is looking into the practices at GM or at its suppliers. But even if the problem is at a supplier, it could cause problems for the embattled automaker, which depends on the flow of parts and supplies from several companies which are already operating under bankruptcy court protections.

The only previous disclosure of a grand jury investigation involving the company in recent filings was a statement by the company that it was complying with a broader industry-wide investigation of the reinsurance business. But this latest criminal probe could further shake investor confidence in GM's ability to manage its business and avoid bankruptcy.

The attention given to the disclosures is also a sign of heightened sensitivity to any problems at GM. Similar disclosures of other huge conglomerates not viewed as embattled might be essentially ignored by investors and analysts.

The good news for GM is that it made the 10-K filing after missing an earlier deadline with the SEC. But the restatement was another sign of turmoil. The already-battered shares of the Dow component were down another 1.3 percent in after-hours trading Tuesday following the latest announcement.

In a statement Tuesday, GM said the restatement affected GMAC's cash flow but not its earnings or balance sheets for the periods reported. Cash flow is earnings plus depreciation and other non-cash charges such as amortization.

On March 15, the day GM missed the original 10-K deadline, the company first disclosed it has encountered some accounting questions involving GMAC. At the time, the company raised its loss estimate for 2005 by $2 billion to give it a net loss of $10.6 billion.

"In concluding the review, GM determined that the cash flows related to certain mortgage activities were not appropriately classified as either operating cash flows or investing cash flows," said a statement from GM on Tuesday. "These changes reduced operating cash flows and increased investing cash flows in each respective period by the same amount."

The finance unit is by far the most profitable operation at General Motors, producing net income of $2.8 billion in 2005, while GM as a whole reported a loss, Reuters reported.

GMAC's mortgage business became its primary profit driver last year, producing $1.4 billion in earnings, compared with $1.1 billion from auto finance, the news agency said.

Still, GMAC's operations have been hampered since GM's debt got cut to "junk bond" status by the major debt-rating agencies, a move that raised GM's cost of raising capital.

A sale of a majority stake in GMAC is seen as the surest way to restore its investment grade rating, while at the same time providing a cash infusion for GM's embattled auto operations.

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For more on GM's accounting headaches, click here.