Toyota Motor Corp. said Monday there are

By ALEXANDRA BERZON And KATE LINEBAUGH

Toyota Motor Corp. said Monday there are “significant inconsistencies” between a California man’s account of how his Prius hybrid accelerated out of control last week and the car maker’s preliminary investigation of the vehicle.

The driver, James Sikes, said he applied heavy pressure to the brake pedal while the car traveled at high speeds in an attempt to stop it. But Toyota disputed that account.

“We believe the vehicle was being driven with the front brakes lightly applied,” Bob Waltz, Toyota’s U.S. vice president for product, quality and service support, said at a press conference in San Diego.

Mr. Waltz said data captured by the car indicated that the brakes and accelerator were depressed about 250 different times during the incident.

Toyota spokesman Mike Michels said the driver would have had to repeatedly press and release the brakes, and press and release the accelerator, to defeat a brake-override system designed to prevent runaway acceleration. The system cuts off acceleration once the brakes are firmly pressed.

“So the on-and-off action would have been required to keep the car going at any kind of high speed,” Mr. Michels said.

Toyota said it tested the accelerator pedal and found it to be working properly. The front brakes showed severe wear and damage from overheating, which could come from repeated light application, Toyota said.

Last week, the 61-year-old Mr. Sikes called 911 and told the operator his blue 2008 Toyota Prius had sped up to more than 90 miles per hour on its own on Interstate 8 near San Diego. He eventually brought the vehicle to a stop after a California Highway Patrol officer pulled alongside Mr. Sikes and offered help via loudspeaker.

“Toyota believes there were serious inconsistencies with the account of event of March 8 and the findings of this investigation,” Mr. Michels said at the press conference. He cautioned that Toyota’s investigation was preliminary and said federal safety regulators continued to conduct their own investigation.

The high-speed drama in California undercut a Toyota effort to discredit its critics and reassure drivers that the Japanese auto maker’s vehicles are safe. Reports of unintended acceleration have prompted Toyota to recall more than six million vehicles in the U.S. and have led to multiple congressional hearings, all of which have damaged Toyota’s reputation as a quality leader.

Toyota lashed out against media reports of the California Prius incident, saying there had been a rush to judgment before the investigation was complete.

“To say this incident was sensationalized would be an enormous understatement,” Mr. Michels said. “Jumping to conclusions is dangerous and investigations should be allowed to take their course.”

As Toyota tries to fight back against its critics new incidents of alleged unintended acceleration keep being reported. The National Highway Traffic Safety Administration is sending experts to a New York City suburb where the driver of a 2005 Prius said she crashed into a stone wall last week after the car accelerated on its own.

Write to Alexandra Berzon at alexandra.berzon@wsj.com and Kate Linebaugh at kate.linebaugh@wsj.com