(Reuters) - A U.S. senator told federal safety regulators he is concerned that they didn't go far enough in a probe that found Toyota Motor Corp's electronics systems did not cause unintended acceleration incidents.
Sen. Charles Grassley, Republican from Iowa, sent a letter, dated Thursday, to the regulators saying a phenomenon known as tin whiskers "may be a cause for concern."
In a statement, Toyota said, "No one has ever found a single real-world example of tin whiskers causing an unintended acceleration event."
Grassley's letter said tin whiskers are "electronically conductive, crystalline structures of tin that sometimes grow from surfaces where tin (especially electroplated tin) is used as a final finish."
Company spokesman Brian Lyons said, "There have been a lot of theories that tin whiskers can cause unintended acceleration. The fact is, they never have."
The NHTSA said on Friday it would carefully review Grassley's letter and respond appropriately.
A NASA report issued in February 2011 as well as findings of an independent scientific panel in January 2012 support Toyota's stance that its throttle systems were not the cause of the unintended acceleration events that prompted the worst safety crisis in the history of Japan's leading automaker.
About 8 million Toyota and Lexus brand vehicles were recalled in the United States in 2009 and 2010, which along with Japan is Toyota's largest market. Toyota is No. 3 in U.S. sales so far this year.
Millions of other Toyota and Lexus vehicles were recalled worldwide. The recalls were not for the electronic throttle systems. Many of them were for floor mats that could cause accelerator pedals to become stuck open.
Grassley's letter cites the NASA report as cautioning that even though NASA found no proof that the electronic throttle control system caused the reported unintended acceleration events, that does not mean they could not occur.
Toyota said that there is no data that suggests that its vehicles are any more prone to "tin whiskers" issues than those of other manufacturers.
"In the unlikely event that tin whiskers cause a short- circuit in the pedal position sensor," Toyota's statement said, "our systems detect the fault, illuminate the malfunction indicator light and put the vehicle into "limp home" mode, allowing the driver to safely move the vehicle to the side of the road as designed.
NHTSA and NASA reports on unintended acceleration can be found at www.nhtsa.gov/ua.
(Reporting By Bernie Woodall)