Toyota Responds to Accelerator Test

Today, Toyota responded to the specific tests conducted by Professor David Gilbert that cast some doubt on the electrical and computer integrity of some of the company's throttle-by-wire systems.

Essentially, Prof. Gilbert tried to show that an electrical short circuit could cause sudden unintended acceleration. Toyota had consistently maintained that such a short circuit was not a real-world possibility. That rebuttal initially seemed weak (never say never), but today the company buttressed its argument by trying to replicate Prof. Gilbert's test and then explaining in detail what they believe occurred and why it could never happen in real driving conditions.

The most important passage in Toyota's statement:

"First, the protective insulation on two separate wires that carry the accelerator pedal position signals to the Engine Control Module must be individually cut or breached. Next, these wires are connected to each other through a 200 Ohm resistor.

This contrivance, by itself, did not cause an increase in engine speed. To cause an increase in engine speed, it is necessary to cut the insulation on a third wire, the 5-volt power supply to the accelerator pedal, and force a low resistance connection between the power supply and the secondary signal wire.

The resulting increase in engine speed is a result of the subsequent artificial and sudden application of the 5-volt power supply to this signal line with the rewired circuit. When subjected to similar unrealistic reengineering and rewiring, the competitive vehicles evaluated by Exponent and Toyota achieved substantially similar results with varying levels of resistances."

The bottom line: Toyota is characterizing this as being equivalent to sending the car's computer modules a false signal that exactly matches a supposedly valid signal (or voltage). While there have been accusations of conflict of interest on both sides, the most disturbing part of the issue seems to be the insertion of the 200-ohm resistor–if that is precisely what Prof. Glibert did.

There are still complaints from Toyota owners who have claimed the company's fixes haven't worked. And there will doubtless be some response from Prof. Gilbert….and considerable legal wrangling to come.

For a more detailed look at the complexity of the problem, see "Complaints About Toyota Fixes."


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About jquain

Technology reporter, writer, and television correspondent, JQ has been covering the computer, communications, and consumer electronics industries for more than 25 years.A contributor to The New York Times, Popular Mechanics, PC Magazine, U.S. News & World Report and many other publications, JQ appears on CBS News television program Up to the Minute and on Fox Business.
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