Getting to the Bottom of Toyota's Sudden Acceleration Problem

Instead of analyzing vehicles with identified failures, the firm hired by Toyota tested several ordinary vehicles and components - like testing healthy people to identify an illness.

By Joel S. Hirschhorn
Published March 09, 2010

As a materials and manufacturing engineer with decades of experience in failure analysis of manufactured products - and as an owner of a Toyota vehicle - I am saddened by the lack of expertise and insight shared with the US Congress and the public about the sudden acceleration problem.

When products fail due to a systemic design, materials or manufacturing flaw, large and statistically significant levels of problems emerge fairly rapidly. This is definitely not the case with the Toyota problem.

With many millions of Toyota models on which even more millions of miles have been driven, if there had been an inherent materials or manufacturing design defect, then we would have seen untold thousands of cases of sudden acceleration. It literally would have been almost a daily event happening all over the country in many Toyota models.

In fact, little more than 1,000 Toyota and Lexus owners have reported since 2001 that their vehicles suddenly accelerated on their own. This is a tiny, minuscule percentage of Toyotas.

This infrequent runaway car problem is not analogous to a serious case of bacterial contamination of a major food product causing many thousands of cases of food poisoning in a relatively short period. It is even more difficult to find the cause.

Nonsensical Guesswork Servicing

Understanding this nature of defects also means that the so-called solutions of replacing floor mats and gas pedals are sheer nonsense. Indeed, it did not surprise me to read recently that there have already been cases of sudden acceleration in cars that had received fixes by Toyota.

More than 60 Toyota owners have complained to the National Highway Traffic Safety Administration about cars already repaired under the two major Toyota recalls, saying they aren't fixed and their throttles can still race out of control.

While recognizing the agony and suffering of sudden acceleration accidents and deaths, it is also necessary to appreciate the statistically rare occurrences of this problem. Only by doing so is it possible to understand that the ultimate explanation - and solution - to the sudden acceleration problem will be a non-systemic flaw or defect in a critical component.

In other words, either a random defect in a material or some unusual and infrequent deviation in a manufacturing process of some critical component.

Only such a situation can logically explain so few sudden acceleration problems in so many millions of cars being operated for many more millions of hours and miles.

Rare Defect, Not Systemic

In my professional opinion, the likely scenario is a defect in a semiconductor chip used in the electronic control system - a defect that was caused by some infrequent flaw in a raw material or manufacturing process that would not show up in routine quality control testing of raw materials or components.

That so many different Toyota models over many years have been found defective signifies the likelihood of a particular problem component made in a specific factory that has been used for quite a while.

Moreover, the defect obviously does not ordinarily impair vehicle performance but only manifests itself under some infrequent conditions, as yet undetermined.

Rita Taylor of Fort Worth, Texas experienced runaway acceleration, took her car to a Toyota dealer, and had the floor mats removed. A few months later she had another frightening runaway episode. Ditto for Eric Weiss in California, who also had a second episode months after the first one and after removing the mats. Others who have not died and kept using their Toyotas have also had repeat events.

Thus, perfectly normal vehicle performance is possible between runaway events.

Accelerator Override System

Make no mistake, the precise cause of such a sporadic event will be incredibly difficult to pin down and even more difficult to remedy. An extremely intense and costly investigation is necessary. It is the classic needle-in-the-haystack problem. If my thinking is correct, it is sheer folly to believe that replacing floor mats or gas pedals can solve the sudden acceleration problem.

However, there is one aspect to the sudden acceleration problem that also is crystal clear and, in some ways, even more aggravating than the acceleration problem.

This is the absence of an override system that absolutely prevents fuel being fed to the engine when brakes are employed while a car is accelerating.

It is gratifying that the US federal government is seriously considering requiring such an override system in all vehicles.

An effective override system might, in the long run, be a faster and more cost-effective solution than chasing-the-defect strategy, especially for retrofitting many millions of vehicles.

Failed Toyota Autopsy

Alternatively, finding the cause of the sudden acceleration problem requires a standard failure analysis methodology: obtain absolutely every Toyota vehicle that has experienced sudden acceleration, and then meticulously examine through microscopic and other types of analysis and testing all critical components of the electronic system (called by Toyota the Electronic Throttle Control System with intelligence).

Think of it like an autopsy.

This does not appear to have been done. To the contrary, the firm hired by Toyota tested several ordinary vehicles and components. One of the primary authors of the Exponent report said they did not examine any vehicles or components that had the unintended accelerations.

This makes no sense whatsoever if the defect is rare and, therefore, its finding that there was nothing wrong was meaningless.

Worse, it was a deception and distraction.

Joel S. Hirschhorn, Ph.D., is the author of Sprawl Kills - How Blandburbs Steal Your Time, Health, and Money. He can be reached through his website: Check out Joel's new book at


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By mikeonthemountain (registered) | Posted March 09, 2010 at 10:20:24

Very nicely explained! If it was an aircraft they'd have every molecule of that vehicle under a microscope to figure out what went wrong. Could it be the typical liability equation of lives vs dollars? Not enough casualties yet? Hopefully they do the right thing and conduct a proper forensic on the faulty vehicles so more families don't have their cars runaway on them!

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By Ryan (registered) - website | Posted March 09, 2010 at 11:52:15

It sounds like they're doing voodoo troubleshooting - never a good idea, even for heisenbugs. If you try random things to make a bug go away and the bug goes away, you're actually worse off than you were before:

  • Since you don't really know what caused the bug, you still don't know what will trigger it again;
  • Your random tweaking may have introduced other bugs that you also can't predict because you don't really understand what the system does.

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By seancb (registered) - website | Posted March 10, 2010 at 12:01:19

my 31 year old carbureted engine has no computer, and no acceleration problems (other than the fact that it does not accelerate fast enough for the leadfoot waiting behind me at an intersection)

it also has no override (thankfully, because in the winter I need to use the gas and the brake at the same time while sitting at a light otherwise it will stall)

it's probably not as efficient as a 2009 toyota though.

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By Kiely (registered) | Posted March 10, 2010 at 15:17:59

"...the absence of an override system that absolutely prevents fuel being fed to the engine when brakes are employed while a car is accelerating."

Sure, but selecting Neutral would be a good start to preventing unintended acceleration.

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By zippo (registered) | Posted March 13, 2010 at 14:57:20

On my 5 year old motorcycle there is a carburetor, not an automated fuel injection system. It's throttle plate is opened not by a computer controlled servo, but by a cable connected to the handlebar grip. This is all very similar to most cars of 20 years ago and removes the possibility of software or electronic hardware failure causing "overspeed", but not obviously mechanical failure. Fortunately it does not stop there. The throttle is closed not by a spring alone as in many older cars (those springs did break from time to time causing a "stuck throttle"), but also by a separate and independent cable to the handlebar grip which actively pulls the throttle closed. Now this system can fail, but the approach of such failure is detectable and preventable with simple routine maintenance.

Should this be neglected and failure occur there is then a 2 layer system to remove electrical power to the ignition system; The ignition key switch, which cuts all power to the bike, and a separate and independent "kill" switch on the handle bar which cuts all power to the engine (but keeps power to the lights and horn). Again, unlike the modern car, these switches are not input devices to a computer but simple mechanical devices located electrically between the battery and the engine.

Could all of this "fail unsafe" simultaneously resulting in an unmanageable overspeed? Sure, but I am not aware that it ever has. I'm certainly not losing sleep over the possibility.

We know that no practical amount of testing of a non-trivial software system can prove it to be bug free, only demonstrate the existence of a bug. I think we can also say that it is "very difficult" to construct computer hardware that operates "fault free" for essentially "no money" (the x hundred dollars that the cars engine control computer and sensors cost).

I doubt that adding another layer of software complexity to the computer system is the path to a truly "robust" solution to the problem.

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By mikeonthemountain (registered) | Posted March 14, 2010 at 11:41:17

This is pretty scary:

They start out saying:

"Federal and Toyota investigators who examined and test drove the car could not replicate the problems Sikes said he encountered, the memo said. The findings raise questions about “the credibility of Mr. Sikes’ reporting of events,” said Kurt Bardella, a spokesman for California Rep. Darrell Issa, the top Republican on the House Oversight Committee that is looking into the incident."

But then a few paragraphs down they say:

"The memorandum obtained by The AP said when investigators placed the Prius up on a lift, they found the driver side front wheel well was dislodged and the brake pads were worn down. “Visually checking the brake pads and rotor it was clearly visible that there was nothing left,” the memo said."

So there is physical evidence that the man burnt out the brakes trying to stop, but he's lying only because they couldn't duplicate the problem? This is really bad. Are more people going to die because they're trying to cover up, perhaps out of frustration because they can't find the cause? What is really going on here?

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By mikeonthemountain (registered) | Posted March 14, 2010 at 11:44:16

... btw I'm not worried because I drive a Toyota, I'm worried because there are ticking time bombs that can careen out of control at any time striking other drivers and pedestrians. If they are trying to cover this up they are committing murder by negligence.

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