WASHINGTON – The National Highway Traffic Safety Administration’s (NHTSA’s) Administrator David Strickland defended the organization’s investigation into unintended acceleration in Toyota vehicles in response to a letter from Senator Charles Grassley (R-Iowa) that questions whether the investigation was “too narrow” in its scope due to a phenomenon called “tin whiskers.”

Grassley’s letter says he received information, supported by documentation, from whistleblowers that raised concerns over the “tin whiskers” phenomenon in the accelerator pedal assembly and other vehicle electronics .NASA’s report defines “tin whiskers” as a phenomenon where “electronically conductive, crystalline structures of tin that sometimes grow from surfaces where tin (especially electroplated tin) is used as a final finish.”

According to Grassley’s letter, NASA’s report found these “tin whiskers” in a Toyota vehicle pedal assembly. In addition, a separate unintended acceleration study of a 2003 Camry conducted in the fall of 2011 found two “tin whiskers” inside.

From there, Grassley’s letter goes on to questions whether NHTSA has definitively determined the cause of unintended acceleration incidents or not. It questions why NHTSA involved NASA engineers in the investigation, whether NHTSA’s personnel lack the expertise to conduct investigations, about NHTSA’s position on “tin whiskers,” and whether the number of vehicles NHTSA and NASA inspected, out of a total of 9,698 complaints, was really enough to determine that “tin whiskers” aren’t a factor in unintended acceleration events.

In response, NHTSA’s Strickland sent a letter to Grassley that explained the steps NHTSA took in the investigation and its reasons for involving NASA. The letter said NHTSA involved NASA specifically to check for the tin whisker phenomenon to determine whether NHTSA investigators had missed anything. NASA’s conclusion, detailed in a report, was that it would take multiple, simultaneous shorts to cause a large throttle opening unintended acceleration event, and that the design of the system in Toyota vehicles can tolerate shorts without that occurring.

In terms of the number of vehicles inspected, NHTSA and NASA actually inspected a total of four Camry vehicles where the electronic throttle control detected a fault, lit the check engine light, and stored a trouble code. According to NHTSA, none of the other complaints showed the effect that type of fault had on vehicle operation, which was (in the four cases) an “abnormal” vehicle response (a “jerk”) when the driver applied the accelerator.

Lastly, Grassley asked a question about what factors contributed to the proposed April 12, 2012, Notice of Proposed Rulemaking (NPRM) related to FMVSS 124, “Accelerator Control Systems.” This rulemaking would require vehicle design changes in order to prevent pedal sticking or entrapment.

Strickland responded by saying the proposal came from the need to change the test procedure, conducted by NHTSA, to define what “disconnection” of an electronic throttle means, the receipt of reported incidents of vehicle pedals being trapped due to mechanical causes (not electronic ones), and crash investigations and analyses of existing data on crashes in NHTSA’s database.

For more information, you can read NHTSA's reports on its website.

By Greg Basich