WASHINGTON (AP) -- The Transportation Department opened an investigation Thursday into brake problems in the 2010 Prius, the latest in a series of safety troubles at Toyota that have confused drivers and strained the Japanese automaker's relationship with U.S. regulators.
Toyota earlier Thursday acknowledged design problems with the brakes in its prized gas-electric hybrid, but said it was still deciding how to inform customers and whether a recall is needed.
The National Highway Traffic Safety Administration, the Transportation Department's safety agency, said it has received 124 reports from consumers about the Prius brakes, including four reports of crashes. The investigation will look into allegations of momentary loss of braking capability while traveling over uneven road surfaces, potholes or bumps.
The U.S. investigation, while preliminary, represents another setback for Toyota, which has been battered with two major recalls in the United States covering millions of vehicles. Those involve gas pedals that can get trapped under floor mats or become stuck on their own and fail to return to the idle position. The safety probes have challenged Toyota's long-standing reputation for building safe, quality vehicles.
The Prius was not part of the recall spanning the U.S., Europe and China over sticking gas pedals in eight top-selling models including the Camry. That recall involved 2.3 million cars in the U.S. alone.
NHTSA said investigators have talked to consumers and conducted pre-investigatory field work. The preliminary evaluation involves about 37,000 vehicles in the United States.
"Safety is our top priority," said Transportation Secretary Ray LaHood. NHTSA said LaHood spoke with Toyota president Akio Toyoda late Wednesday and was assured by the executive that Toyota was taking the safety concerns seriously.
Toyota said in a statement it would fully cooperate with NHTSA's investigation.
The U.S. investigation came after the Japanese government ordered Toyota to investigate brake problems in the Prius, the world's best-selling hybrid. Toyota said it had already corrected problems with the antilock brake system in Prius models sold since late last month, including those shipped overseas.
The new version of the gas-electric Prius hybrid went on sale in the U.S. and Japan in May 2009.
Paul Nolasco, a company spokesman in Japan, said the time lag for brakes kicking in felt by drivers stem from the two systems in a gas-electric hybrid -- the gas-engine and the electric motor.
When the car moves on a bumpy or slippery surface, a driver can feel a pause in the braking when the vehicle switches between the traditional hydraulic brakes and the electronically operated braking system, he said. The brakes work if the driver keeps pushing the pedal, he said.
Toyota acknowledged the brake problem while reporting a $1.7 billion profit for its October-December quarter.
NHTSA said it opens 100 investigations every year and there are currently 40 open defect investigations, three of which involve Toyota. NHTSA said its defect and compliance investigations have resulted in 524 recalls involving 23.5 million vehicles during the past three years.
Shares of Toyota traded in the U.S. fell $2.09, or nearly 3 percent, to $71.40 in late morning trade Thursday. Since Jan. 21, when the U.S. recalls were announced, the stock has lost about 22 percent.
Toyota senior managing director Takahiko Ijichi defended the automaker's quality standards.
"We have not sacrificed the quality for the sake of saving costs," he said. "Quality is our lifeline. We want our customers to feel safe and regain their trust as soon as possible."
Toyota for the first time gave an estimate of the costs of the global gas-pedal recall. The $2 billion total represents $1.1 billion for repairs and $770 million to $880 million in lost sales.
Toyota is expecting to lose 100,000 in vehicle sales because of the recall fallout -- 80,000 of them in North America.
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Kageyama reported from Tokyo.
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