The debate over the role of tin whiskers in Toyota's unintended acceleration case has returned, and government administrators are expected to answer more questions on the subject this week.
Even after the National Highway Traffic Safety Administration (NHTSA) declared in 2011 that there was no electronic cause for Toyota's problems, the debate had quietly continued. It rose to prominence again this month, when a US senator stepped in.
"Recently, whistleblowers have provided my office with information, supported by documentation, which raises concerns that the scope of the NHTSA and NASA investigations may have been too narrow," Sen. Charles E. Grassley (R-IA) wrote in a letter (PDF) to NHTSA Administrator David Strickland on July 12. The letter went on to pose questions about the agency's methodology, and it called for answers to be delivered by July 26.
Toyota's Matrix is one of the vehicles recalled during the automaker's "unintended acceleration" studies. (Source: Toyota)
Tin whiskers -- small metal dendrites that sometimes form on electroplated tin -- are an important topic for design engineers, because they can cause short circuits and arcing in electrical equipment. In Toyota's case, tin whiskers were considered a potential culprit in the "unintended acceleration" claims that grabbed headlines three years ago.
Much of the debate over tin whiskers died down in February 2011, after Secretary of Transportation Ray LaHood called on teams of NHTSA and NASA engineers to search for the cause of Toyota's problems. "The verdict is in," LaHood declared emphatically after the scientists reached their conclusion. "There is no electronic-based cause for unintended high-speed acceleration in Toyotas. Period."
After that conclusion was announced, the National Academy of Sciences said that all available data indicated there was no electronic or software problem on the Toyotas.
Still, the buzz about tin whiskers continued in some quarters, especially after a separate team of NASA scientists published a study (PDF) of Toyota accelerator pedals on the Internet in September 2011. The scientists said they found tin whiskers in an accelerator assembly, and "a tin whisker induced short was responsible for the failure of a 2003 Toyota Camry Accelerator Pedal Position (APP) Sensor based on a Dual Potentiometer Design."
In his letter, Grassley cited that study and its author, Henning Leidecker of NASA Goddard, to support his claim that more questions needed to be answered.
In response to the latest volley, Toyota officials argued that tin whiskers may cause failure of pedal sensors, but they've never caused unintended acceleration. "We know that tin whiskers can form -- we've never said they couldn't," Brian Lyons, a spokesman for Toyota, told us. "But when pedals fail -- for whatever reason -- the vehicle enters into a fail-safe situation, a limp-home mode."
Lyons also said that the September 2011 study specifically linked tin whiskers to sensor failure in the accelerator assemblies, not to unintended acceleration.
When reports of unintended acceleration originally surfaced, Toyota engineers examined multiple potential culprits: the accelerator's friction lever, heater condensation, corrosion, electronics, and floor mats. Toyota has since examined the mats, shortened the pedals, lengthened the friction lever, added a spacer, and changed the linkage materials. It also employs a brake-throttle override on its vehicles to cut off gas flow if the brake and accelerator pedals are depressed simultaneously.
Until Grassley sent his letter to the NHTSA, the focus had shifted away from electronics and toward floor mat entanglements. In June, the NHTSA mandated a recall of 154,000 more Toyota vehicles for problems associated with "unsecured or incompatible floor mats."
Most resisitive throttle position sensors will have two sensors, and for a given throttle position each sensor sends a different value. With the different values for a given throttle position, the ECU can determine when there is a problem and go into the limp-home mode if required.
Bring lead back to electronics. Rohs is out of control on some critical elements that are needed for reliability and safety. Lead is exempt from censure in Avionics and should be also in automotive.
My personal belief is lead from improperly discarded batteries is the real issue. Not the trace amounts such as solder from PCBs. I think there are more naturally occuring toxic elements in soil.
I agree with your wife. Toyota was unfairly "bashed" in many ways. The bottom line with the horrific crash of the ES350 in San Diego was a jammed carpet mat, a mat from an RX350 that had been installed inadvertently by a hired hand at the dealership. The crash had nothing to do with tin whiskers or any computer malfunction.
I also would like to comment about German vehicles. Their overall reliability, according to Consumer Reports, is still well below that of many Japanese vehicles. Their performance and customer "pampering" lure in buyers who often overlook the inconvenience of having to take their vehicles in for not-very-infrequent repairs.
Whiskers had been found and photographed by NASA scientists. There is no problem with the fact of whiskers.The problem is that we live in the world that covers the truth.They should just say:we found a problem.Bring the cars and we will correct it.Thing is that mat takes no time, changing design and construction of a module takes a lot of time.They are back on top and they will take care of their customers like they always did.They are probably using a supply of service parts now, which is a temporary fix, because they are defective like originals....unless problem is already fixed in those.
To other friends: We are talking about cars that were built after ROHS (no lead) rules.Toyota is not an exception.All electronics fails left and right and one year warranty disappeared from the market and is replaced with 90 years warranty.
A known fact is that most of electronics manufacturers give their products 4 years life span, which means that garbage can is a destination after 4 years.How about your parents, or grandparents 15 year old Zenith TV set.....well that's an ancient history.
There are expensive methods to slow it down , but it includes special print on super-epoxy masks and increase of distance between PC board traces...and it is not inn today's world.Everything has to be tiny......and it breaks after 30 -90 days.Nothing , except metal inhibitors can stop whiskers' growth.You are absolutely right.
It's with interest and surprise to see the debate about the recent problem being addressed by Toyota. It was a surprise that it still being discussed. It,s also a surprise that the cause is still unknown or that a probable cause has not been articulated. Is it possible that tin whiskers caused the problem? The answer is yes but what is the probability that it is the cause. I would suggest that it's very low. Although we do not fully know what triggers the mechanism, there are a number of factors that have to be in place for it to occur such as humidity, material stress, humidity, etc. Also', we also know how to get rid of it So what is the big issue? If whiskers is the problem, why the debate?
I would suggest that perhaps a different mechanism may be at work --- Fretting Corrosion. This mechanism is a result of low amplitudes of movement (as low as 0.001 to 0.003 of an inch) that can occur with all material systems including tin, nickel, copper and even gold (gold wears exposing under plate or other non-noble substrates). This mechanism does create momentary interruptions in electronic systems(we've been involved with this issue for since the 1970's). When a contact moves on a "bad" spot it will cause a fault. As motion continues the contact will move off the "bad" spot to a "good" spot and the fault will disappear. These faults can be as fast as 2 nS. Unfortunately, fretting is not predictable.
I will stop at this point. My frustration is that everyone is jumping on Toyota trying to fix the cause that is being described as tin whiskering. However, where is the conclusive data to show that it is. Fretting has a higher probability but there is no data to prove this either. Why can't Toyoata indicate what they have investigated with data to prove or disapprove the condition so we can move on to the next situation?
Nice article, Chuck. If tin whickers might be the failure that caused the unintended acceleration, that means a failed component could be the culprit. I would think the discovery is a matter of determining what component failure (if any) would result in unintended acceleration.
Hi Chuck-IAG... I'm actually a MOPAR fanboy and have owned a Dodge 400, Dodge Caravan, Dodge Stratus, Chrysler Sebring Convertible, Dodge Durango, and our current toy hauler is a 5.7L Jeep Grand Cherokee. I'm not a mechanic, but I have a code reader and a socket set and have switched out my share of thermostats, temperature sensors, oxygen sensors, and throttle-position sensors. We have put over 300K miles on the Corollas and the most I have had to switch out is light bulbs (thankfully).
The 2003 1.8L Turbo Automatic VW Convertible New Beetle was a different beast altogether. My wife fell in love with the styling and she is still heavily mourning its loss. My comments here were not to start a flame war, but on the topic of Design, the VW was in its own league. I only learned that Volkswagen was the parent of Audi, Bentley, Bugatti, Lamborghini, Porsche, and Ducati after we purchased the Bug from a reputable local dealer that sells only late-model used cars. What I didn't expect was that after the Bug started to lose sensors and electronic controllers that there are practically no user-serviceable parts and that we would need to take it to the dealer and pay Porsche repair prices for a VW. After a $9000 quote from the dealership to replace the trans at 75K we traded it in as salvage.
My overall point was that my experience with Toyota is not only have they been the most reliable cars we have owned, they are also the easiest to maintain -- designed with repair in mind. -- Rather than designed for exacting tolerances and then handed over to highly-skilled mechanics to fix when broken.
Perhaps some day when I have a Lamborghini repair budget on hand, I will consider VW again...
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