Toyota Motor Corp said it had found no flaw with its throttle controls as it seeks to dismiss an external study critical of its electronic safety systems.

The conclusions, announced at a news conference on Monday, marked an attempt by the automaker to reassure consumers it has safety issues under control. Toyota is working to win back sales seven weeks into a recall crisis that has tarnished its reputation.

But in developments that underscored the continuing pressure on Toyota, a Michigan judge ordered the automaker's top two U.S. executives to appear for a deposition and a congressional panel told it to surrender a 2006 memo from employees in Japan warning of risks to quality controls.

Toyota called its news conference to discredit what it said were mistaken conclusions being drawn from a study of its accelerator controls by David Gilbert, an auto engineering expert at Southern Illinois University.

Toyota has recalled more than 8 million vehicles worldwide for mechanical problems with its accelerator assembly that can cause sticking and for the risk that floormats could trap an accelerator.

Unintended acceleration in Toyota and Lexus vehicles has been linked to at least five U.S. crash deaths since 2007. Authorities are investigating 47 other crash deaths over the past decade.

The U.S. National Highway Traffic Safety Administration has also said it is looking into more recent complaints from drivers who say they suffered acceleration problems even after their vehicles were fixed in the recent recall effort.

Those complaints have been seen by some as further evidence that Toyota could face a problem with vehicle electronics or software that could go beyond the mechanical fixes it has announced under its recalls.

But Toyota spokesman Mike Michels said the automaker had found that post-recall accelerator complaints appeared to reflect a small number of cases where repairs at dealerships had not been performed correctly.

We're confident in our electronic throttle control systems, Michels said.

TOYOTA: NO EVIDENCE OF FLAW

Gilbert told a congressional panel in late February that he had found a way to simulate a flaw in Toyota's accelerator controls so that the vehicle could surge forward without a fault code being generated for an onboard computer Toyota has designed as a safeguard.

But Toyota said an outside review of Gilbert's findings by a Stanford University expert and engineering consulting company Exponent had not found evidence that conditions described by Gilbert could occur in real-world driving.

Chris Gerdes, a professor of mechanical engineering at Stanford and director of the university's Center for Automotive Research, said Gilbert had essentially rewired Toyota's accelerator system to generate his results.

Fundamentally, you cannot rewire a circuit and expect it to behave as designed, Gerdes told reporters.

Gilbert said he planned to visit Exponent's test facilities next week and expected to complete a review of the information it had presented in the next few weeks.

I am pleased that further examination of these safety and acceleration issues is taking place, and I look forward to participating in this process, he said in an email to Reuters.

JUDGE ORDERS TOYOTA TESTIMONY

Toyota is facing dozens of lawsuits stemming from its recalls and both sides in that litigation have been working to line up expert witnesses.

Gilbert has received some funding from the Safety Research and Strategies, a safety advocacy that has in turn taken funding from trial lawyers with cases pending against Toyota.

For its part, Toyota has hired Exponent and has provided financial assistance to Stanford's auto safety center.

Toyota and Exponent said they were continuing to test other explanations for unintended acceleration that would go beyond the problems it has identified.

Separately on Monday, a Flint, Michigan area judge ordered Toyota's top two U.S. executives -- Yoshimi Inaba and Jim Lentz -- to appear for questioning for lawyers for the family of a woman who was killed in a Camry crash in 2008.

Guadalope Alberto died when her 2005 Camry surged out of control. Her family is suing Toyota. Lawyers for Toyota had argued that lower-level executives should be allowed to answer questions from Alberto's lawyer, but the judge ordered Lentz and Inaba to appear, said Hike Heiskell, a lawyer for the Alberto family.

Also on Monday, Rep. Edolphus Towns, a New York Democrat who chairs the House Oversight and Government Reform Committee, asked Toyota to turn over a letter Toyota employees in Japan sent to management in 2006 detailing safety concerns. Towns made the request in a letter sent on Monday.

The October 2006 letter, addressed to then-president Katsuaki Watanabe from a splinter union called the All Toyota Labor Union in the wake of a recall scandal in Japan, had warned that a failure to address quality concerns could ultimately threaten the company's survival.

Among the causes of the quality slippage, the group blamed the fall in the number of experienced staff in favor of contract workers, the longer working hours and the aggressive pursuit of cost reductions.

The letter appeared on the 20-member union's website. Toyota had no immediate comment.

(Additional reporting by Chang-Ran Kim in Tokyo; Editing by Carol Bishopric and Anshuman Daga)

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