The National Highway Traffic Safety Administration is refuting accusations made by a former administrator that the agency may have dragged its feet in order to bolster sales of the Chevrolet Volt after the battery pack of one of the plug-in hybrids caught fire three weeks after the car was subjected to a side-impact crash test in May. The incident was not made public by NHTSA or General Motors until November.

Read: Feds Investigating Chevrolet Volt Fire

Joan Claybrook, a former NHTSA administrator who stepped down as president of the consumer rights group Public Citizen in 2008, told the Automotive News on Monday, "not to tell them anything for six months makes no sense to me. NHTSA could have put out a consumer alert and I think they should have done so."

Claybrook added: "I believe they delayed it because of the fragility of [Volt] sales."

The fire took place in a parking lot, where the damaged Volt had been left by the agency in the same condition it was in after the test. In a statement issued to FoxNews.com, NHTSA said that since the fire occurred near other vehicles, the agency “needed to determine through careful, forensic analysis whether the Volt was the actual cause of the fire -- and, if so, what the implications were for safety.”

“Once the Volt was identified as the potential source,” the NHTSA added, “the agency had a responsibility to ensure that the May crash test was not an anomaly, given that subsequent vehicle crash tests by both NHTSA and General Motors did not result in the same outcome.”

The investigation was made public on November 11, and in mid-November NHTSA conducted tests on the Volt’s battery pack itself, damaging and rotating several examples to simulate a rollover accident. One emitted smoke and sparks, and another caught fire a week after it was tested. The agency announced the findings the following day, while maintaining that the car “is safe and does not present undue risk as part of normal operation or immediately after a severe crash."

The investigation into the cause of the fires is ongoing, and the focus is on the cooling fluid that is used in the pack, which may form crystals when exposed to air, causing an electrical short. GM says that its post-crash protocols call for the pack to be drained if it is damaged, something NHTSA did not do after the initial test, as it had not been informed of the procedures at the time.

Read: Source Says Coolant Leak is Likely the Cause of Chevy Volt Fires

Reuters is reporting that engineers are close to a solution to the problem, which will cost the automaker less than $1,000 per car to fix. In the meantime, GM has agreed to buy back about two dozen Volts from buyers concerned about the fire risk, and has offered loaner cars to every Volt owner until the situation has been resolved.

The House Oversight and Government Reform Committee plans to hold a hearing on the Volt battery issue in January, which will take up the topic of how NHTSA has handled the investigation.

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