Now that the National Highway Traffic Safety Admin station has closed its investigation into vehicle fires in the Chevrolet Volt, General Motors is left to clean up the public relations damage.

The media counter-attack started Wednesday with newspaper and television advertisements that coincided with GM chief executive Dan Akerson's appearance at a Capitol Hill hearing on the investigation.

"I do think there has been collateral damage [to the Volt's reputation]," Akerson said during the hearing. "We're going to have to work hard to get it back and I think today is a great start."

The hearings, which focused on the timeliness of NHTSA's response to the fires, provided an opportunity for Akerson to fully explain what happened with the car, he said, and what GM had done in response.

NHTSA and GM agree that the potential for fire posed little, if any real risk to Volt drivers. The fires that sparked the investigation happened seven days to three weeks after side impact crash tests. As part of the test the vehicles were rotated upside down spilling battery coolant onto exposed wiring.

GM engineers devised additional metal structures that are being added to Volts, both on the assembly line and to cars already on the road. These structures are designed to broadly spread impact forces, reducing the risk of a coolant leak.

It was after GM announced it was making those changes that NHTSA decided to close its investigation.

But media reports had already caused confusion and concern among potential buyers, GM spokesman Rob Peterson said. Which is why GM launched an aggressive marketing campaign Wednesday.

"The Volt as an innovation rather than a political punching bag," said Peterson. "That's a story that's been lost in recent weeks."

In the newspaper ads, which appeared in 19 daily newspapers, GM quotes from NHTSA's own public statement at the conclusion of the investigation.