GMAC, the money-losing lender labeled too big to fail by the US, has used government guarantees to slash its borrowing costs and undercut profitable lenders, lifting its bond prices by 80 percent since March.

GMAC sold $3.5 billion of federally backed bonds in June at a 2.2 percent yield, 65 percent below its average borrowing costs in the first quarter.

The firm’s bank, renamed Ally in May, cut the rate it pays on 12-month certificates of deposit by half in the past year to 2 percent.

The lender reports second-quarter results today following losses in six of the past seven periods. The Detroit-based firm, which took $13.5 billion in US bailout funds, turned to cheaper government financing after 20 months of declining auto sales and rising credit losses from soured mortgages hurt its ability to line up private investments.

GMAC’s average global cost of borrowing has been above 5 percent since 2005 when the three biggest credit-rating companies cut its debt to junk.

Funding costs peaked at 6.53 percent at the end of 2008 before slipping to 6.21 percent in the period ended March, according to the company.