The investigation, which called on NASA scientists to examine whether the acceleration was due to faulty electronics, pointed instead to two mechanical faults.
NASA engineers found "no electronic flaws in Toyota vehicles" that would "create dangerous high-speed unintended acceleration incidents," the Department of Transportation said, concluding a 10-month review.
The probe analyzed 280,000 lines of code used to run Toyota's vehicles for flaws and examined whether electromagnetic radiation might have played a role.
Instead the accidents, which prompted the recall of eight million vehicles worldwide, were blamed on mechanical problems with a "sticking" accelerator pedal and floor mats.
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