In Understanding Toyota Sudden Acceleration, materials engineering expert witness Joel S. Hirschhorn writes:
When products fail due to a systemic design, materials or manufacturing flaw, large and statistically significant levels of problems emerge fairly rapidly. This is definitely not the case with the Toyota problem. With many millions of Toyota models on which even more millions of miles have been driven, if there had been an inherent materials or manufacturing design defect, then we would have seen untold thousands of cases of sudden acceleration. It literally would have been virtually a daily event happening all over the country in many Toyota models. But, in fact, little more than 1,000 Toyota and Lexus owners have reported since 2001 that their vehicles suddenly accelerated on their own. This is a tiny, minuscule percentage of Toyotas….
In my professional opinion, the likely scenario is a defect in a semiconductor chip used in the electronic control system. A defect that was caused by some infrequent flaw in a raw material or manufacturing process that would not show up in routine quality control testing of raw materials or components. That so many different Toyota models over many years have been found defective signifies the likelihood of a particular problem component made in a specific factory that has been used for quite a while. Moreover, the defect obviously does not ordinarily impair vehicle performance but only manifests itself under some infrequent conditions, as yet undetermined.
Excerpted from americanchronicle.com.