Toyota Motor appeared to have "consistently dismissed" the possibility that electronic throttle failures could cause unintended acceleration, according to lawmakers who also questioned statements by the company on its big recalls.

US Representatives Henry Waxman and Bart Stupak, chairmen of the House Energy and Commerce Committee and the panel's investigative subcommittee, respectively, also said on Monday that the government's response to complaints about unintended acceleration in Toyota vehicles appeared to have been "seriously deficient."

Waxman and Stupak were responding to a preliminary review by committee investigators of tens of thousands of documents submitted to the panel by Toyota and the National Highway Traffic Safety Administration ahead of a hearing on Tuesday.

Lawmakers from two House committees and a Senate panel are investigating US recalls of 6 million Toyota cars and trucks for potential problems related to unintended acceleration.

The recalls in October last year and January this year have focused on loose floor mats that can become trapped under the accelerator and gas pedals that do not spring back as designed.

Regulators believe floor mats are related to two crashes that killed five people in 2007 and 2009, and are investigating up to 29 other reports of fatal accidents that allege unintended acceleration. No fatalities are tied to the so-called "sticky pedal" problem, officials have said.

Congress wants to know whether the safety steps were timely and adequate. Lawmakers also want to know whether Toyota and NHTSA thoroughly considered over the years the possibility that electronic throttles could be behind some complaints.

Toyota has said the throttle system now used throughout its lineup of cars and trucks is sound, and the government has never found any problems.

Toyota said it was reviewing the letter from Waxman and Stupak to its US sales chief Jim Lentz, who is scheduled to testify at the hearing, and continues to cooperate with the committee.

Earlier on Monday, Toyota told reporters on Monday that it had conducted numerous tests on its electronic throttle system going back 6 to 7 years, and to date was unable to find any link to unintended acceleration.

Transportation Department officials confirmed receipt of the committee's letter to Secretary Ray LaHood and defended the highway safety agency. LaHood spokeswoman Olivia Alair said in a statement that NHTSA was well versed in electronic throttle issues and has the expertise to conduct such investigations.

LaHood will appear before the Waxman's panel on Tuesday.

The House Oversight and Government Reform Committee will hold a separate hearing on Wednesday at which Toyota President Akio Toyoda is scheduled to testify along with LaHood and others.

Waxman and Stupak said the committee reviewed a representative sample of complaints supplied by Toyota and other documents related to unintended acceleration.

Their letter said documents provided to the committee "reveal that Toyota's frequent response to these complaints was to dismiss the possibility of failure in its electronic throttle control system."

The committee said it appeared Toyota never conducted a "systematic investigation" into whether electronic defects could lead to unintended acceleration. Also, the lawmakers criticized as too narrow an independent study commissioned by the company that found no problem with its throttle system.

Lawmakers also said Lentz's public statements that Toyota was confident the recalls would address issues of unintended acceleration conflicted with private explanations other Toyota officials gave Energy and Commerce Committee staffers.

The committee was equally critical of NHTSA, saying in the letter to LaHood the agency lacked internal tools to evaluate potential defects in vehicle electronic controls.

NHTSA told the committee staff that it does not employ any electrical or software engineers. – Reuters