John Rockefeller, the chairman of the senate commerce committee, said US regulators had also failed to move aggressively in their investigation of cases of unintended acceleration.
He disclosed documents showing that Toyota's senior US executive had warned back in 2006 that the quality of the company's vehicles was slipping, and warned of growing problems with US regulators.
"A year and-a-half later, Chris Tinto, Toyota's top safety official in Washington, tried to warn his superiors in Japan that quality problems were growing and, in his words, 'we have a less defensible product that's not typical of the Toyota that I know'," Rockefeller said.
Among the issues that have emerged from Toyota's quality issues is that the carmaker's regional entities did not communicate enough with each other to allow earlier identification of issues.
At the hearing Toyota executives said the company would provide US safety regulators electronic data recorders to enable them to read the "black boxes" in vehicles to determine the cause of accelerator problems.
Yoshimi Inaba, the president of Toyota in North America, said the company would be delivering three of the devices on Wednesday, and hoped to make the data more accessible to other systems by the middle of 2011.
He said Toyota would dispatch its engineers to the US to train technicians on the use of the devices.
Over in Europe, Andrea Formica, Toyota Europe's vice-president, apologised to European consumers for the global recall of 8.5 million vehicles worldwide since October for sticky accelerator pedals, faulty floor mats and glitches in braking software that have stained its reputation for quality.
"All the vehicles currently being produced meet the highest safety and quality standards," Formica added as Toyota launched its new global hybrid Auris at the Geneva motor show on Tuesday.
Formica's apology follows similar acts of contrition in China and the US by Akio Toyoda, the company's president, in the past week.