Toyota is confident that its electronic throttles are sound and not behind instances of unintended acceleration that led to huge recalls and lawsuits, the company’s US sales president said.

In written testimony submitted to Congress, Jim Lentz also said Toyota had serviced more than 3.5m vehicles – around half the vehicles recalled between October 2009 and January 2010 for equipment and mechanical issues linked to the acceleration problems.

Toyota Europe, meanwhile, said it expected to have completed 90% of the work modifying accelerator pedals in some models and reprogramming Prius brake software by July.

Lentz told the House of Representatives Energy and Commerce Committee: “We are taking major steps to become a more responsive, safety focused organisation. Our entire company has mobilised to ensure that Toyota vehicles are safe and reliable for our customers.”

On Tuesday, Toyota paid a US$16.4m fine to settle allegations by US regulators that the company had been slow to act on one of the recalls.

However, some members of the Energy and Commerce Committee are not convinced that Toyota’s fixes in recalled vehicles address all questions about unintended acceleration.

The committee has demanded information about Toyota’s electronic throttle systems and whether they could be at the root of acceleration problems that authorities have said could be linked to a number of crash deaths since 2000.

Lenz said: “Toyota has never discovered or been provided with any evidence that (electronic throttles) can cause unintended acceleration in a real world scenario.”

Toyota has hired an engineering consulting firm, Exponent, to analyse its throttle systems. This analysis will be reviewed by an independent scientific committee before the NHTSA decides how to proceed.

The analysis and review could take more than a year.

Toyota carried out inspections on about 2,000 vehicles looking for issues related to unintended acceleration and found a host of possible causes, but none of them were the result of its electronic throttle control, according to Lenz.

Floormats that hadn’t been replaced in earlier recalls, unfamiliarity with how vehicles act when resuming cruise control and multiple stacked floormats were all found to be causes of customer concerns, he added.

“As a result of these evaluations, we now understand that we need to improve our communication with customers about the features, characteristics and normal functions of our vehicles.”