DETROIT -

General Motors chairman and CEO Daniel F. Akerson will testify before a Republican-led House Committee on Wednesday. 

The committee is challenging the Obama administration's investigation into Chevy Volt batteries that caught fire last year, raising questions about whether the government's partial ownership of  GM created a conflict of interest. 

The report by the Republican staff of the House Committee on Oversight and Government Reform said it was "deeply troubling" that safety regulators waited several months before telling the public that a Volt battery caught fire three weeks after a government crash test. The fire happened in June but was not made public until November -- "a period of time that also coincides with the negotiation over the 2017-2025 fuel economy standards," the report states, adding that it was possible that those negotiations "incentivized NHTSA to remain silent on the issue."

But in a recent letter to committee chairman Darrell Issa, R-Calif., National Highway Traffic Safety Administration Administrator David Strickland said that the agency's investigation into the Chevy Volt "is completely unrelated to the fuel economy standards rulemaking."

The committee was set to hold a subcommittee hearing on the issue Wednesday. The Associated Press obtained a copy of the report ahead of its official release.

In an email Tuesday, NHTSA spokeswoman Lynda Tran said that following the June fire, the agency needed to determine through careful forensic analysis whether the Volt was the actual cause -- and if so, what the implications were for safety -- and that took time.

"If at any time during this process we had reason to believe that vehicle owners faced any imminent safety risk we would have made that point known to the public right away," she said.

NHTSA began studying the Volt last June after a fire broke out in one of the cars three weeks after it was crashed as part of safety testing. Two other fires related to separate safety tests occurred later, and NHTSA opened an official investigation into the vehicle on Nov. 25. The government ended its investigation last week, concluding that the Volt and other electric cars don't pose a greater fire risk than gasoline-powered cars. The agency and General Motors Co. know of no fires in real-world crashes.

But some critics have criticized the government's response, accusing it of having a conflict of interest because the government still owns 26.5 percent of the company's shares, and because the administration has touted electric cars. Wednesday's subcommittee hearing of the House Oversight and Government Reform was titled, "Volt Vehicle Fire: What Did NHTSA Know and When Did They Know It?"   "Questions have been raised as to whether or not GM receives special deference from the administration because of its status as a ward of the state," the committee report states, adding, "the Obama administration has tied the political reputation of the president closely to the success of GM generally, and to the Chevy Volt specifically." The report also accuses NHTSA officials of not cooperating with its investigation, and of being unprepared to respond to car battery risks.

Both Strickland and Akerson were scheduled to testify at Wednesday's hearing.

In written testimony, Akerson said that testing by government regulators resulted in fires "after putting the battery through lab conditions that no driver would experience in the real world."

The company advised Volt owners to return their cars to dealers for repairs that will lower the risk of battery fires. GM hopes that, by adding steel to the plates protecting the batteries, it will ease worries about the car's safety. The cars are covered by a "customer satisfaction program" run by GM, which is similar to a safety recall but allows the carmaker to avoid the bad publicity and federal monitoring that come with a recall.

"The Volt is safe," Akerson said