WASHINGTON - A congressional committee has asked Toyota Motor Corp. and its Exponent Inc. consultant to produce any findings about possible electronic causes of unintended acceleration in advance of a May 6 hearing, Automotive News reported.

House Energy and Commerce Committee Chairman Henry Waxman requested “any documents, including reports, analyses or other communications, describing the results of Exponent's work for Toyota related to unintended acceleration or electronic throttle-control systems.”

Exponent, based in Menlo Park, Calif., has been hired by Toyota to study possible links between electronic defects and unintended acceleration in Toyota vehicles.

Toyota has cited Exponent's preliminary findings that there is no such link in defending its long-standing position that any problems with speed control are due not to the vehicles themselves but to floor mat interference or sticky gas pedals.

Waxman, D-Calif., had criticized Exponent's preliminary work for Toyota in February, saying it lacked scientific rigor and relied on an indefensibly small testing sample.

Waxman's letter today, co-signed by Rep. Bart Stupak, D-Mich., chairman of the committee's oversight panel, also asked for all correspondence between Toyota and Exponent about the scope of the contractor's work and all contracts between the two.

The letter asked that Toyota Motor Sales U.S.A. President James Lentz and Exponent CEO Paul Johnson testify at the May 6 hearing, which was disclosed for the first time in the letters to each.

"Toyota is more than willing to meet with the committee and discuss the ongoing testing related to our electronic throttle-control system, as well as the steps we are taking to improve our quality-assurance processes," spokeswoman Cindy Knight said. "Nothing is more important to us than the safety and reliability of the vehicles our customers drive."

An Exponent spokeswoman declined comment.

Federal regulators are conducting a scientific review of possible electronic links to unintended acceleration in Toyota's and other automakers' vehicles.