As US Congressional investigators dig further into potential electronic problems in runaway Toyotas, the auto maker is facing fresh safety concerns, recalling 600,000 Sienna vehicles over rusting spare tire holders.

The recall came as House investigators said they would hold another hearing in May to review possible electronic problems in runaway Toyotas. The Japanese auto maker has recalled more than 8 million vehicles worldwide because of faulty accelerator pedals, humbling a car company long known for its quality and safety.

Company leaders vowed to respond quickly to the safety concerns.

Separately, Toyota last Friday said its engineers in Japan had duplicated the same results of tests that led Consumer Reports to issue a rare "don't buy" warning on the 2010 Lexus GX 460 over rollover concerns. Toyota responded by halting sales of new GX 460s and conducting tests on all of its sport-utility vehicles.

Lexus spokesman Bill Kwong said the company was evaluating potential remedies for the GX 460 but it was "too early to speculate (on) the details of the remedy and its timing."

Toyota said its latest recall covered the 1998-2010 model year Siennas with two-wheel-drive that have been sold or registered in 20 cold-climate states and the District of Columbia. Toyota said rust from road salt could cause the carrier cable that holds the spare tire to rust and break, allowing the tire to tumble into the road. The problem could threaten the safety of other drivers.

Toyota said it was unaware of any accidents or injuries. The US National Highway Traffic Safety Administration said it received six complaints of spare tires falling off Siennas.

The company said it was working on a fix. In the meantime, customers will receive a notice telling them to bring their vehicle to a dealership for an inspection.

Steve St. Angelo, Toyota's chief quality officer for North America, said the company was providing free inspections of the spare tire carrier cable across America.

Democratic lawmakers remain focused on the spate of recalls affecting the company. Henry Waxman, chairman of the House Energy and Commerce Committee, and Bart Stupak, a subcommittee chairman, said they plan a May 6 hearing to look into potential electronic causes of sudden acceleration in Toyota vehicles.

Toyota has said it has found no evidence of electronic problems, attributing the issues to sticking gas pedals and accelerators that can become jammed in floor mats.

Toyota last Friday said it was "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."