The computer system seems most likely culprit. Problem appears to be intermittent and so difficult to reproduce. Likely hardware causes include poor ground. This can cause a circuit to be completed through a resistance. The resistor may be any other component through which a path to ground can be established. The diagnosis would involve introducing a low resistance in the current circuit and seeing how it behaves.
The long term fix would most likely be a redesign of the circuit to ensure no parallel pathway exist to ground.
What’s your theory on the cause(s) of unintended acceleration in Toyotas?
I would like to hear from engineer readers about what they think might be causing the unintended acceleration problem in Toyotas. Please post your comments below.
Non-engineers are encouraged to comment, too. Journalist me falls into this category, but not to brag, I wield a mighty wrench. My engineering bona fides are as chief editor at two engineering magazines.
You might also read an excellent story in this past Sunday’s Washington Post, which offers various theories for Toyota’s problems and reinforces a post I did March 5 about government regulators inability to protect us from technology-inspired schemes and mechanisms.
I happened to be talking about high frequency trading, a technology-based stock trading method, but the same point applies. Regulators and especially lawyers/politicians cannot possibly grasp the application of new technologies at the pace with which they are coming at us. It’s that simple. It’s that complex. It’s that scary.
The article’s author is journalist Frank Ahrens, who happens to have a degree in mechanical engineering so he inherently understands the challenge Toyota faces in finding the problem causing unintended acceleration.
Frank Ahrens. credit: PBS.org
“Members of Congress are generally lawyers and politicians, not engineers. But they are launching investigations and creating policies that have a direct impact on the designers and builders of incredibly complex vehicles — there are 20,000 parts in a modern car — so there are some basics they should understand. Chief among them: The only way to credibly figure out why something fails is to attempt to duplicate the failure under observable conditions. This is the engineering method,” writes Ahrens.
Amid an ocean of variables, he explains how the company might go about its investigation and the questions it might ask:
– “Road conditions where accidents happened (Is it a rain/snow/sleet/temperature problem?)
– Where the cars were made (Is it a parts or assembly problem?)
– How the cars were drawn up (Is it a design flaw? If so, is it a mechanical or electronic flaw? Or a combination?)
– How the cars were tested (Did the company fail to anticipate a series of events that would lead to a flaw?)”
He explores another very obvious suspect: Did the operator have his or her foot on the wrong pedal? It’s hard to imagine anyone would do this for more than a few minutes or seconds, but then again, we do have the Darwin Awards, don’t we. One expert cited in the story says that’s almost always the culprit.
Read some of the 327 comments to the story that have apparently swamped the Post’s web site (comments are closed…never seen that before). Many are humorous and cynical. Also, several engineers weigh in with their opinions which could be summed up this way: “It’s the software, stupid.”
I’ve posted a sampling below with embedded links to the page which carries the full comment.
“– the problem’s in the computer code (likely firmware) - all this posturing with floor mats and accelerator pedals is a disgrace.
–Need a fix, Toyota? Just KISS. Simply install an alarm system that alerts drivers every time you cut a deal with NHTSA.
– I have a BS in aeronautical engineering and 48 years of experience programming computers. The type of problem under discussion sounds like a classic “race condition” - hard to reproduce, but very real. When the action taken by a computer is determined by the outcome of a “race, that is, which external event “gets there” first - wins the race - you have a race condition. This may involve hardware or not, but almost always involves software.
– This is all BS. Toyota knows the problem, they just won’t admit it. Toyota is learning that its simply not a good business practice to put profit above human life.”
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