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Musings on Toyota

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For a few months now, Toyota has been in the news with accellerator problems, which lately seems to be getting deeper every day.  There are also possible political angels to this, but I won’t focus on that right now.

Working in the automotive field, I have seen enough autos to know that Toyota makes a pretty decent product.  They tend to built pretty solid, with pretty reliable engines.

Their current problems seem to be coming from a ‘drive by wire’ system that is becoming popular with manufacturers.  What that means is that there is no old-fashioned throttle linkage from the pedal to the engine.  Instead, a sensor is built into the pedal, feeding the computer that information, which the computer uses to open a valve or set of valves on the engine via an electrical signal.  Several upsides with this type of system include fewer moving parts, tighter computerized control of engine management (resulting in better fuel milage and performance), less likelihood of a mechanical cable binding, breaking, or otherwise wearing out.  The downside, of course, is that any component can fail, even electronic computerized ones.

As there seems to be no definitive answers on what exactly is failing in these cars, most of what I read and hear of it is speculation.  Realistically, there are only three components that can fail:  The position sensor on the pedal itself, the computer module, or the throttle valve assembly.  Since I hear mainly about the pedals, I’m going to assume the problem lies in that area.

In my experience with sensors, even those with no moving parts, I know they can all fail, sometimes spectacularly, and often times in ways the computer self-diagnostics can not detect.  In the case of the pedal, the computer knows the feedback will be between X and Y volts, X being idle, and Y being pedal to the metal.  As long as that signal is in that range, the computer will think that you the driver are causing  the signal to be what it is, not realizing there is a problem.

Ever have your gas gauge suddenly shoot to “Empty?”  Or “Full” for that matter, even though you know it can’t possibly be right?  It’s the same sort of circuit, what is known as a rheostat, or variable resistor.  Same as the volume knob on a radio.  Ever have an old radio go full volume and won’t turn down?

Until the problems are totally solved, I would like to offer Toyota, or any other company using this sort of throttle system, a suggestion.  A small reprogram of the engine control computer can help negate the dangerous conditions if the sensor shorts out high.  Program the module to watch for, say, 85% or 90% throttle or higher.  If it stays there for longer than, say, 10 seconds, the computer will override the pedal, and cut back the throttle valves.  Another 10 seconds, and the computer would drop it to idle speeds, allowing you to stop and pull over.

Sometimes as a driver, you will run the accellerator at wide open, such as passing, getting up to speed on entrance ramps, and other situations.  But rarely, I would think, would you keep it there longer than 10 seconds, especially considering that most cars these days will be well over 60 miles per hour in that time.  If by chance you do need hard accel longer than that, simply letting up the pedal, and pressing it again would reset that counter, assuring the computer that yes, you DO want full throttle.

If you as a driver are ever in a situation where the engine seems to be running away, please be extremely careful.  Always be aware of your situation.  If this happens to you, I suggest that you watch the road carefully, place the transmission in Neutral.  This disengages the drivetrain to stop further accelleration.  A rev-limiter will prevent the engine from racing too high and destroying itself.  You can then firmly control the steering, and apply brakes and safely getting to the side of the road.  Once stopped, you can then shut off the engine.  And call a tow truck!

Be careful out there!  People tend to forget that cars are two-ton weapons, with numerous systems that must function together.  Those systems can, and do fail.  No matter how well something is designed and built, or how long you’ve never had a problem, things WILL break.  So please, again, be very careful.  Your life and others can be at risk.

Written by James Lee

February 23, 2010 at 09:45

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