NEW YORK (CNNMoney.com) -- The National Highway Traffic Safety Administration announced Thursday it is opening a formal investigation into problems with the braking system of Toyota's Prius hybrid.
Toyota has yet to announce a recall of the Prius, it's fourth-best selling vehicle model in the United States and the best-selling model in Japan. But it has admitted to a software glitch that is causing problems with its braking. It said it is looking further at the best way to repair the problem.
The investigation involves only 2010 model year Prius hybrids, which went on sale in the middle of last year. There are only 37,000 of those vehicles on the road, according to the agency.
The Prius, which is built in Japan, is not one of the eight models that was affected by two recalls recently to fix problems with sticking gas pedals. All of those models were built at North American plants.
NHTSA said its Office of Defects Investigation has received 124 reports from consumers about problems with the Prius brakes, including four reports that involved crashes and two which resulted in injuries. No fatalities have been reported. Investigators have spoken with consumers and conducted preliminary field work.
Late Wednesday, U.S. Transportation Secretary Ray LaHood spoke with Toyota (TM) president, Akio Toyoda, who reassured him that Toyota takes U.S. safety concerns seriously and puts safety at the top of the company's priorities, according to NHTSA's statement.
Toyota had only limited comment on the probe.
"We have heard about NHTSA's intention to begin an investigation. Toyota will cooperate fully with NHTSA's investigation," the company said in a statement.
Even if the solution ends up being a relatively simple and inexpensive software adjustment, the Prius braking problems come at a bad time for Toyota, which has seen its prized reputation for quality and safety badly damaged by the recalls and the news attention given to them.
The company has estimated that the problem with the gas pedals will cost it about 100,000 sales this year, and $2 billion in repair costs and lost revenue.
Other experts say the problem could be more long-lasting if consumers who once trusted the Toyota brand decide to shop elsewhere.
Toyota said Thursday that the Prius problem is a "disconnect" in the vehicle's complex anti-lock brake system that causes less than a one-second lag before the brakes start to work. At 60 mph, though, a vehicle will have traveled nearly another 90 feet before the brakes begin to take hold.
The company also said it changed the braking system software in January for vehicles built since then. But it has yet to determine how to fix the brakes of vehicles already on the road.
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