WASHINGTON - Congressional investigators have widened their probe of defects in Toyota Motor Corp. vehicles yet again, asking five leading automobile insurers if they had notified U.S. regulators of unintended acceleration reported by consumers as far back as 2000, according to a report by Automotive News and Reuters.

House Energy Committee Chairman Henry Waxman, D-Calif., on Tuesday sent letters to Allstate Insurance, Farmers Insurance Group, GEICO, Progressive Group and State Farm Group asking for copies of their communications with the National Highway Traffic Safety Administration about Toyota defects. He gave a Feb. 17 deadline for responses.

The panel is trying to determine the history of Toyota's efforts to identify and address its defects, as well as the effectiveness of NHTSA's oversight over the years.

The letters, also signed by Rep. Bart Stupak, D-Mich., chairman of an oversight subcommittee, followed a Tuesday Washington Post report saying State Farm Insurance had notified NHTSA numerous times starting in 2007 about an unusual number of cases of unintended acceleration.

“We are interested in learning whether your company has issued similar warnings to the agency,” the congressional letters said.

In 2007, NHTSA was conducting an investigation of Toyota acceleration that led to a recall of 55,000 floor mats.

Both the House Energy Committee, which has a hearing scheduled for Feb. 25, and the House Oversight Committee, which postponed a hearing until Feb. 24, are investigating defects in Toyota vehicles.

The Energy panel initially requested documents from Toyota and NHTSA dating back to 2000 that might shed light on the causes of unintended acceleration in Toyota vehicles. Last week, the committee asked about possible connections between the speed-control problem and the braking problems reported on the Prius.

The Oversight panel last week asked Toyota whether its problems might be caused not only by floor mat entrapment and sticky gas pedals, as the company has asserted, but also by electronic defects, which the automaker has denied.