Oct. 7 (Bloomberg) -- Toyota Motor Corp.’s Tundra pickup truck is being investigated by regulators for “severe” frame corrosion that may cause brake failure, a week after the company said a floor-mat flaw would spur its biggest U.S. recall.

The U.S. National Highway Traffic Safety Administration said yesterday it’s looking into 20 complaints on model-year 2000 and 2001 Tundra pickups alleging broken brake lines and spare tires that came loose. The inquiry covers about 218,000 vehicles, the agency said on its Web site.

Toyota is already recalling about 3.8 million vehicles including 2007-2010 Tundras because the floor mats may jam down the accelerator pedal. The recall and Tundra inquiry may add to strains on the world’s biggest automaker after its U.S. sales plunged 28 percent in the first nine months of 2009 amid a recession that pummeled demand.

“Time will tell whether these are isolated incidents,” David Champion, director of automobile testing for Consumer Reports magazine, said in an interview. The recall and inquiry “are sort of worrying signs that maybe they’ve grown too big too quickly and brought out too many cars to be able to maintain their stellar reliability histories. That being said, they are still one of the best manufacturers out there.”

Toyota, manufacturer of the top-selling Camry, said in a filing published today on the safety agency’s Web site that it’s making the recall on vehicles with the floor-mat glitch even though it hasn’t determined that they have a “safety-related defect” as defined by the federal government.

‘Grasping for Salvation’

John Hanson, a Toyota spokesman, had no immediate comment on the Tundra investigation. Toyota’s U.S. sales unit is based in Torrance, California.

The carmaker reached an agreement with plaintiff lawyers in Texas over documents about the “crashworthiness” of its vehicles. The accord eliminates the need for a hearing scheduled for today, according to a letter from Toyota’s lawyer to the judge that was filed yesterday in court in Marshall, Texas.

The company is “grasping for salvation” as it predicts a second straight annual loss, President Akio Toyoda said last week.

“We have to listen to our customers and make better cars,” Toyoda said in a speech to journalists in Tokyo Oct. 2. The 53-year-old grandson of Toyota’s founder became president of the Toyota City, Japan-based carmaker in June.

Toyota extended warranties last year for some 1995-through- 2000 Tacoma pickups in the U.S. because of reports of excessive corrosion of the trucks’ frames.

Toyota held its lead this year in a benchmark U.S. survey of new-vehicle quality released in June by research firm J.D. Power & Associates.

Toyota’s American depositary receipts rose 15 cents to $77.42 at 4:04 p.m. in New York Stock Exchange composite trading. They have gained 18 percent this year.

To contact the reporter on this story: Angela Greiling Keane in Washington at agreilingkea@bloomberg.net

Last Updated: October 7, 2009 16:40 EDT