General Motors Co expects to have U.S. federal safety officials resolve their investigation of delayed fires in the Chevrolet Volt electric car sooner rather than later, a top executive said on Monday.

The National Highway Traffic Safety Administration launched a probe of the Volt's battery pack in November after fires in the vehicle's battery occurred days after the car was involved in federal safety tests last year.

NHTSA administrator David Strickland said on Sunday he was comfortable with GM's proposed fix for the problem, but their investigation has not been closed. He added he hoped the investigation would be concluded soon.

We're very optimistic with NHTSA, based on the feedback we've gotten, GM's global product development chief Mary Barra told Reuters at the Detroit auto show.

While Barra said she did not know exactly when federal officials would close the probe, she added: We're a short time frame, not an extended, protracted period away from a resolution.

Last week, GM said it had developed a fix for the Volt that would better protect the vehicle's 400-pound lithium ion battery by adding steel reinforcements and taking other steps to prevent coolant fluid from leaking and triggering a fire.

GM previously said it had shared its engineering and test results with NHTSA and was optimistic its proposed fix would allow the U.S. safety agency to close its investigation.

GM has said it would begin making the repairs at Chevy dealerships in February. The automaker has sold about 8,000 Volts in the United States, just over half of the target it had set for the past year.

A relatively quick solution to the Volt safety issue would mean that GM could avoid a time-consuming and costly distraction and a recall of a key halo vehicle.

GM has made the Volt the symbol of its determination to seize a leadership position in fuel economy and green technology and its engineers have been racing to respond to a safety investigation by U.S. regulators since late last year.

GM's Chief Executive Dan Akerson said on Sunday at a different event that the company may have to adjust production rates for the Volt.

We're going to match production with demand, Akerson said when asked about meeting Volt sales targets. There are new variables in the equation, so we'll see. We've been responsive to our customers' needs, and, at the end of the day, that will serve us well.

The Volt's battery is designed to provide a range of about 40 miles on electric power. The plug-in hybrid also has a gasoline-powered 1.4-liter engine to provide additional range after the battery has been drawn down.

The plug-in hybrid costs $40,000 before a $7,500 federal tax credit in the United States.

Barra said on Monday the same technology will be used in Volt's next couple model years, but future models would try to cut costs on the battery so changes were likely, just not for technical reasons. We're very confident in our cells, she said. We're also very confident in the cooling system for the battery. (Reporting by Ben Klayman, editing by Maureen Bavdek)

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