Instead, the problems seemingly were caused either by sticky pedals or by a faulty design where the pedals could be caught on badly fitted floor mats, concludes a report issued by the National Highway Traffic Safety Administration (NHTSA), the DOT agency that at the behest of Congress.

After a series of highly publicized and sometimes deadly accidents, Toyota recalled nearly 8 million vehicles between 2009 and 2010 that could potentially suffer from the problem of accelerating rapidly and beyond the driver's control. While Toyota and the NHTSA initially blamed bad accelerator design and badly placed floor mats for the incidents, members of Congress, in a series of hearings, grilled both Toyota and NHTSA executives that the failures could have been caused by electronics interference, badly designed electronics or bad supporting software code.

As part of the study, NASA engineers analyzed more than 280,000 lines of code that manage Toyota's electronic braking system; they also examined the underlying electronic circuitry. They looked for bugs or other potential flaws that could lead to unintended throttle opening.

"NASA found no evidence that a malfunction in electronics caused large unintended accelerations," said Michael Kirsch, principal engineer at the NASA Engineering and Safety Center, in a statement.

In a second test, another group of NASA and NHTSA researchers subjected vehicles' braking systems to large amounts of electromagnetic radiation, in order to test another widely circulated hypotheses that the malfunctions occurred due to electronic interference. They found that the braking systems were immune from such interference, however.