A U.S. government investigation into Toyota safety problems has found no electronic flaws to account for reports of sudden, unintentional acceleration.

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Toyota Motor Corp.'s head, Akio Toyoda, speaks to reporters in Nagoya, Japan, in December 2008 before the recall crisis began. (Katsumi Kasahara/Associated Press))

Transportation officials and engineers with NASA say two mechanical safety defects previously identified by the government — sticking accelerator pedals and gas pedals that can become trapped in floor mats — are the only known causes for the reports of runaway Toyotas.

Toyota has recalled more than 12 million vehicles globally since late 2009 to address sticking accelerator pedals, gas pedals that became trapped in floor mats, and other safety issues. The recalls have posed a major challenge for the world's No. 1 automaker, which has scrambled to protect its reputation for safety and reliability.

Transportation Secretary Ray LaHood says the department's 10-month study has concluded there is no electronic-based cause of unintended high-speed acceleration in Toyotas.

"Our conclusion, that Toyota’s problems were mechanical, not electrical, comes after one of the most exhaustive, thorough and intensive research efforts ever undertaken," LaHood said in a statement.

A preliminary part of the study, released last August, also failed to find any electronic flaws based on a review of data recorders, or vehicle black boxes.

Toyota's safety issues received broad attention from the government after four people were killed in a high-speed crash involving a Lexus near San Diego in August 2009.

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Toyota master service technician Mike Blomberg inspects a gas-pedal assembly removed from a Toyota in Springfield, Ill., as part of the company's 11-million-vehicle recall. ((Seth Perlman/Associated Press))

The National Highway Traffic Safety Administration received about 3,000 reports of sudden acceleration incidents involving Toyota vehicles during the past decade, including allegations of 93 deaths. NHTSA, however, has confirmed just five of them.

The company has already implemented a host of new designs in its vehicles, including a brake override system that cuts the throttle when the gas and brake pedals are deployed at the same time. The company has already paid a record $48.8 million in fines for its handling of the crisis.

In Tokyo on Tuesday, Toyota reported a 39 per cent slide in quarterly profit but raised its full-year forecasts for earnings and car sales. It's a mixed picture for the automaker, which is enjoying booming sales in high-growth markets in Asia, Africa and South America, while facing lingering safety worries in the key U.S. market.

Toyota's New York Stock Exchange-listed stock had been trading lower on the bad earnings news but was up more than four per cent, to $89 US, in the minutes following the release of the safety probe's findings. 

With files from the Associated Press