In this Feb. 4, 2010, file photo, a sign assuring customers that the car has… (Seth Wenig / Associated…)
WASHINGTON — A U.S. senator has raised concerns about a government investigation of sudden unintended acceleration problems in Toyota vehicles, saying the probe might have erroneously ruled out the company's electronic throttle control system as a cause.
Sen. Charles E. Grassley (R-Iowa) said whistle-blowers recently have provided his office with information suggesting that the investigation by the National Highway Traffic Safety Administration, with the help of NASA engineers, "may have been too narrow."
In a letter sent Thursday to NHTSA Administrator David Strickland, Grassley asked for detailed information about the investigation and whether vehicles were tested for the presence of an electronic phenomenon known as "tin whiskers" that could have been the cause of unintended acceleration.
"This is a serious issue," Grassley wrote. He noted that NASA engineers said just because they did not find proof that Toyota Motor Corp.'s electronic throttle control system caused the reports of unintended acceleration "does not mean it could not occur."
A NHTSA spokeswoman said the agency was reviewing the letter. Toyota dismissed Grassley's concerns.
"There is no problem with the electronic throttle control systems in Toyota vehicles — and all the scientific evidence confirms it," the company said in a statement.
The 2009 crash of a Toyota Lexus ES 350 near San Diego triggered millions of recalls by the Japanese automaker.
Investigators believe a floor mat in the vehicle was improperly installed and might have trapped the accelerator pedal, causing the car to race down California 125 at more than 100 miles per hour before crashing and bursting into flames. The accident killed off-duty California Highway Patrol Officer Mark Saylor and three family members.
The crash and subsequent Los Angeles Times stories sparked a flood of complaints about sudden acceleration in Toyota vehicles. The automaker recalled 4.4 million vehicles to fix the floor mat problem and millions more to fix sticking gas pedals and other issues.
NHTSA brought in NASA engineers to investigate whether electronic defects or software code errors caused the sudden acceleration. In early 2011, NHTSA and NASA said their 10-month probe found no such evidence.
The agencies concluded that the only defects that could cause the acceleration problem were mechanical problems — specifically floor mats that could jam the gas pedal and sticky accelerator pedals.
But Grassley said tin whiskers "may be a cause for concern" in the acceleration issue. The NASA report described tin whiskers as "electronically conductive, crystalline structures of tin that sometimes grow from surfaces where tin (especially electroplated tin) is used as a final finish."
Grassley said the NASA report found evidence of tin whiskers in one Toyota pedal assembly that caused a short circuit. Such a short, the report said, means the electronic system "may be vulnerable to a specific second fault condition that could theoretically lead" to unintended acceleration, Grassley wrote.
But Toyota said Thursday that "no one has ever found a single real-world example of tin whiskers causing an unintended acceleration event."
"Toyota's systems are designed to reduce the risk that tin whiskers will form in the first place and multiple robust fail-safe systems are in place to counter any effects on the operation of our vehicles in the highly unlikely event that they do form and connect to adjacent circuitry," the Toyota statement said.
If a short circuit takes place, Toyota's systems are designed to detect it, trigger the malfunction indicator light and put the vehicle into "limp home" mode, which enables the driver to safely move the vehicle to the side of the road, the company said.