A fix for Toyota’s problem. A hypothesis that explains the facts: a way towards solutions.

Toyota claim that it is a sticky accelerator mechanism that is causing unwanted and unexpected acceleration in their cars.  I think this is unlikely and here is why.

I have watched all the witness accounts of this problem in Toyota vehicles on the ABC News site.  Now one of these vehicles spontaneously accelerated while going down hill with the driver’s foot off the accelerator pedal.  So a sticky accelerator does not explain what this driver experienced.

Now it is valid to ask if a retired critical care physician like myself has any business posting about a problem like this.  I would plead that physicians are trained and should posses critical analysis  skills, and quickly be able to put a hypothesis together that explains all the facts.

In addition I have worked on cars and engines since my preteen years.  I work on antique and modern engines, and I’m familiar with the components of engine controls.  In addition I have had an over riding interest in electronics, and have put big systems together and I’m familiar with some aspects of circuit design and do my own service work.

In addition my son Andrew is an electrical engineer who graduated summa cum laude from the University of Minnesota.  He has reviewed this hypothesis and finds it more plausible than statements from Toyota.  We also have a vested interest.  He owns a Toyota Camry and a RAV 4.  I own a Toyota Camry.

I have managed to find a copy of the  Toyota throttle circuit in block diagram at least

As you can see it is a servo type of motor with Hall effect control.

Now I came upon this post where a mechanic on eHow says the opening of the PVC valve opens at a bad place on Toyota engines and sticks up the throttle body.

Now if the PCV valve is putting oil deposits in the area of the Hall sensor, this could easily cause the Hall effect device to send erroneous information the the ECM and explain why this problem is so prevalent in so many Toyota models.

Now if that is the problem there are two potential steps Toyota could take to remedy the problem.  When the break light is activated, a voltage should be taken off that to a relay or preferably a MOS FET switch to interrupt the signal from pins 66 and 80 of the PCM to pins 3 and 5 on the throttle body.  Now if the PCV valve effluent is gumming up the throttle body, then the throttle body should be redesigned to have the PCV valve breath into the intake manifold like on every other engine I know of.  The reason for the latter is that if the mechanism is gummed up in the throttle body then breaking power to the throttle body servo motor would not work.

The only fly in the ointment I see here is that the throttle body air flow control looks rather nasty and over complicated from the photographs.  Instead of the usual brass butterfly rotating against spring closure, this Toyota design appears to have a geared louver type of control, and cheap plastic gears at that.  I have a suspicion it might not close with power interrupted to the throttle body servo motor, like the usual arrangement would.  If that is the case, then Toyota would have to totally redesign the throttle body to make a break override be fail safe and operate independently of ECM failure.

The problem has now been documented to occur over a nine year period and seems to involve 2005 models preferentially for some reason.  So the cost to Toyota could be enormous.  If the throttle does not close at zero voltage to the throttle body motor, then this would require a new throttle body design, a new ECM module, and modification and or replacement of the throttle body motor.  This would likely cost more than older and or high mileage vehicles are worth.

If the throttle closes at zero voltage to the servo motor then the fix could be relatively simple.

Questions journalist should be asking Toyota.

1).  How will changing the throttle mechanism prevent random acceleration going down hill when the accelerator was not depressed?

2).  Does the throttle close with no power applied to the throttle servo motor?

3).  Will you quickly provide all throttle control parts, circuit details and software for immediate peer review?  If not why not?

This is I think a very dangerous situation.  I think it is valid question to ash whether or not Toyotas should be grounded until this problem is solved.

Now my hypothesis is very unlikely to be correct in every detail, but I would bet the cause and solution is something along these lines.

Leave a Reply