TOKYO -- Toyota Motor Corp., under fire from fresh quality complaints about its popular Prius hybrid, said today it conducted a software fix to address reports of slipping brakes.
But the world's biggest carmaker didn't notify customers at the time of the change. And it says it is still uncertain how to handle the thousands of Prius vehicles that were sold before the fix.
The problem occurs in the third-generation Prius, which went on sale in the United States, Japan and Europe last year. Transportation agencies in the United States and Japan have been compiling dozens of complaints that the car's brakes give way under certain conditions.
Japan's Ministry of Transportation has ordered Toyota to investigate the problem and consider a recall if a defect is found. The ministry has logged 38 complaints since July.
A computerized search for the 2010 Prius in the online database at the National Highway Traffic Safety Administration generated at least 102 brake-related complaints against the car.
At a hastily called press conference early today to address the mounting complaints, Toyota Managing Officer Hiroyuki Yokoyama said the slipping feeling is caused by a lag time in the shift between the car's regenerative braking system and the antilock braking system.
The phenomenon occurs mostly on slippery or bumpy roads, and complaints rose in December when icy conditions triggered more frequent application of ABS braking in the cars.
"When ABS comes into play, you may feel a little bit of slip, but if you continue to apply the brake it will work," Yokoyama said. "It may cause customers a little unease."
Toyota updated the software in late January to reduce the lag time in cars now coming off the assembly line, Yokoyama said. At the time, Toyota was focused on implementing a fix as soon as possible after the complaints came in, he said.
Toyota is studying whether the old braking pattern is a safety risk. But he said that the braking performance still falls within legal guidelines, he added.
"We want to come up with a countermeasure to inform our customers, so we would like to be allowed some time and come up with a conclusion as soon as possible," Yokoyama said.
The U.S. complaints accounted for at least two injuries. Drivers typically complain about losing braking ability - often while driving over bumpy roads - or feeling the brakes give way.
A report filed Feb. 1 reads: "While braking, if I hit potholes, the car speeds up from loss of braking action, even thou (sic) I am still pushing on the brake pedal."
Another complaint filed in September 2009 said the driver injured her neck when the brakes failed on her Prius and she collided with another vehicle.
News of the fresh investigation comes as the world's largest automaker struggles to rein in a recall crisis aimed at fixing incidents of sudden acceleration in some of its vehicles. Since last fall, Toyota has recalled 8.1 million vehicles worldwide - more cars than it sold last year.
Problems with the latest generation of the Prius, which went on sale in the United States and Japan last year, would be another blow. The green halo surrounding the popular hybrid is largely credited for Toyota's image as a leader in environmentally friendly technology.
In Japan, the Prius is the best selling car.
Japan's Transportation Ministry has asked Toyota to provide a report on the problem, a ministry official said. Two brake incidents resulted in crashes, and two injuries were reported.
"It is necessary to check whether the complaints are based on users' feeling or problems with the car," the official said. "If it is based on the latter, Toyota needs to issue a recall."