An independent study conducted by researchers at the University of Maryland’s Center for Advanced Life Cycle Engineering (CALCE) demonstrates that, contrary to NASA’s conclusions, an electronic cause for the sudden unintended acceleration problem in Toyota vehicles is not just probable, but highly likely.
In conducting their analysis of Toyota’s engine control systems, CALCE researchers Bhanu Sood, Michael Osterman, and Michael Pecht did agree with NASA scientists who found that “tin whiskers” were present in the accelerator pedal units of every potentiometer they examined. But whereas NASA relied on an analysis of warranty data provided by Toyota’s defense expert Exponent to conclude that the tin whiskers did not present a safety hazard, the CALCE scientists found them to be “a cause for concern.”
Tin whiskers are crystalline structures, many times thinner than a human hair, that often form on the tin solder and emanate on the surface of printed circuit boards, causing shorts / current leakage paths and electronic malfunction.
While the National Highway Traffic Safety Administration exonerated Toyota’s electronics after the NASA report, CALCE researchers found as many as six tin whiskers on one potentiometer type accelerator pedal position sensors (APPSs), and concluded “the potential for a tin whisker shorting failure was 140/1 million. Considering the number of vehicles on the road, it is expected that this would present a significant safety hazard.”
Moreover, the CALCE researchers also found that tin whiskers could form in the Engine Control Modules (ECM) of Toyota vehicles, because Toyota used tin-lead solder and tin plating where devices were connected to the circuit, which operates various automotive components much like a computer.
“As previously discussed, tin-fnished leads can grow tin whiskers which can lead to unintended electrical shorts,” Osterman wrote. “We know whiskers can form on tin finished terminals,” he said. “In this case, Toyota has tin plating in a rather sensitive area, where the system relies on changes in resistance to provide a signal for acceleration.”
The findings contradict the report NHTSA released in February concerning the electronic throttle control systems in Toyota, in which Transportation Secretary Ray LaHood asserted, “There is no electronic-based cause for unintended, high-speed acceleration in Toyotas.”
According to the CALCE scientists, “It is highly likely that tin whiskers could induce a failure that is later undetected. For this reason, best practices for electronics design stipulate that tin not be used as a plating material.”
Based on their findings, the CALCE panel found NHTSA’s conclusions irresponsible. “It is very questionable why the National Highway Traffic Safety Administration, with a stated mission to ‘save lives, prevent injuries and reduce economic costs due to road traffic crashes, through education, research, safety standards, and enforcement activity,’ has not come out with a requirement that no electronics use pure tin as a material component, since the potential for tin whiskers presents an unreasonable and unnecessary risk.”