Toyota President Akio Toyoda has apologised to the US Congress and Toyota owners in the United States for safety problems that have led to deaths and worldwide recalls of vehicles.
Mr Toyoda has apologised for the recall of 8.5 million vehicles for accidents which occurred.
But under questioning on Wednesday, he insisted no faults had been discovered with the electronics of any of its vehicles.
Mr Toyoda pledged to give his "full cooperation" to the US government investigation.
He said the company's priorities had become confused during its rapid expansion.
Mr Toyoda said safety will be Toyota's top priority from now on.
Earlier, House Oversight and Government Reform Committee chairman Edolphus Towns said Toyota and regulators had "failed their customers" on safety.
The BBC reports the reputation of Toyota has been severely damaged by major problems across a range of vehicles.
The main issues have been faulty accelerator pedals, accelerator pedals getting stuck in floor mats, and a problem with braking systems on hybrid models.
The recall has cost the company more than $US2 billion.
Mr Toyoda is the grandson of the company's founder. In pre-prepared remarks, he said he took a personal responsibility for improving the quality of Toyota cars.
Congress also heard from Toyota Motor USA chief James Lentz on Tuesday.
Under questioning, he agreed that about 70% of complaints about unintended acceleration remained unexplained.
Domestic inquiry also
The Japanese government is to investigate reports of unintended acceleration of Toyota vehicles.
Transport Minister Seiji Maehara said the government would review 38 cases reported in Japan over the past three years.
He said the investigation would focus on Toyota, but would also include other carmakers.
