WASHINGTON -- U.S. safety regulators, responding to an inquiry by Sen. Charles Grassley, R-Iowa, stood by their original assessment that sticky pedals caused Toyota Motor Corp. cars to accelerate unintentionally and struck down the possibility that an electrical problem was behind it.
In a letter to Grassley, the National Highway Traffic Safety Administration said Thursday that it had explored "in detail" the effects of so-called tin whiskers -- a crystalline growth on a metallic surface that could cause electrical interference with the pedal -- and found no evidence that it was a contributor to the unintended acceleration incidents.
NHTSA maintains the likely cause was "pedal misapplication."
"We do not believe that tin whiskers are a plausible explanation for these incidents," the agency wrote in response to questions Grassley posed this month in a letter to NHTSA.
Grassley, the ranking member of the Senate Judiciary Committee, said he had received documents from whistleblowers about NHTSA's joint investigation into the Toyota problem, which led to the recall of millions of vehicles worldwide.
He said the information provided to his office raised concerns about whether regulators' investigation was "too narrow" in scope.
A 10-month investigation by NHTSA and NASA found no electronic defect in Toyota models. The agencies blamed the incidents on pedals that became stuck or caught under floor mats.
NHTSA reaffirmed its finding in its response, noting that while a small number of incidents were discovered in which tin whiskers may have caused a "jumpy" throttle, none had led to sustained or dangerous acceleration. The condition stopped as soon as the driver release the pedal, NHTSA said.