Toyota gas pedal problems

As I understand it, the accelerator pedal in these toyotas are not
connected to the engine via mechanical linkages - but instead the pedal
position is sensed by a sensor and communicated to the engine control
computer which actuates a servo motor to control engine RPM.

If this is correct, then the problem is either:

a) the pedal sensor becomes faulty and reports incorrect pedal position
(ie - sensor reports that the driver is calling for high engine RPM)

b) the pedal return spring mechanism does not work properly, so the
pedal gets stuck in the accelerate position (and the sensor
accurately reports this pedal position to the computer)

I know that floor mats have been implicated as potentially causing (b),
in which case it could still be argued that the pedal return spring is
not sufficiently strong to overcome floor-mat interference.

What I find incredible is that when either (a) or (b) happens, that the
computer does not also recognize that the driver is also pressing the
brake pedal and make a decision to over-ride the call for high engine
RPM and thus drop the engine to idle RPM. This behavior should be
mandated by the DOT / NHTSA for "drive-by-wire" accelerator-pedal
systems. When presented with conflicting information, the computer
should err on the side of safety.

If the above control pattern was implimented, then if the brake-switch
is faulty then the driver can't accelerate the car, but he can still
control it and bring it to a safe stop.

If drive-by-wire systems are going to be deployed like this in passenger
cars (presumably because they require less mechanical engineering effort
to design, construct and install) then there has to be a recognition
that electric sensors, connections and wires can fail in ways that
mechanical solutions can't or don't, and hence a tradeoff has to be made
that can result in inconvienence to the owner if the control computer
takes corrective (but safe) action based incorrect inputs.

As a result of this Toyota debacle, I will make extreme efforts to
insure that my next car will not have this drive-by-wire accelerator
pedal mechanism.

Does anyone know which car brands (other than Toyota) have this design?

 

In other words, why didn't they implement the system to fail safely.

I agree 100%.

You know, there's a reason that air brakes work the way they do--with
the air pressure holding the brakes OFF, such that if the air pressure
fails, the brakes are ON.

Fail safe. It's a good idea.

 

I'm not sure there are many new cars that use throttle cables anymore.

Electronic Stability Control (ESC) and Traction Control (TRAC)
effectively require that the PCM have full control over throttle
openings. A mechanical cable makes ESC and TRAC harder to implement.

ESC seems to be universal now:
<http://www.tc.gc.ca/eng/roadsafety/tp-tp14651-vs200701-table_names-754.htm>

If the sensor is faulty, the system's fail-safe defaults to idle.

There is no problem with the sensors themselves.

That's what's happening. The new metal-bar fix prevents the stickiness.

That's hard to square with reality.

That a look at the picture on Transport Canad'a website regarding this
issue:
<http://www.tc.gc.ca/eng/roadsafety/tp-tp14665-v200701-menu-241.htm>

No spring would lift /that/ pedal, I think.

Toyota is changing the PCM programming to kill power if the brake and
gas are pressed at the same time.

My thinking? People with winter boots or with big feet will accidentally
hit gas and brake at the same time in traffic and end up getting
rear-ended. I'm not sure Toyota can win this one no matter how hard
they try.

 

The claim is that there is a binding in the mechanism that prevents the
return spring from returning the pedal in the desire manner. I've seen an
illustration of the piece that they are adding to correct this issue, but I
can't understand how it will fix the problem. I am hoping to get a good look
at a "repaired" unit.

It is my understanding that Toyota is going to implement this sort of fail
safe system at least on some cars.

Ed

 

Feds look at Toyota electronics as source of acceleration defects

February 2, 2010 - 4:21 pm ET

WASHINGTON -- The U.S. Department of Transportation is looking into whether
Toyota Motor Corp.'s problems with unintended acceleration can be traced to
defects in the electrical controls rather than just the mechanical problems
cited by the automaker, a Transportation official said today.

"We're not finished with Toyota and are continuing to review possible
defects and monitor the implementation of the recalls," Transportation
Secretary Ray LaHood said in a statement.

When asked whether the federal review includes possible electrical problems
with Toyota vehicles, a Transportation official who asked not to be
identified responded in an e-mail, "Yes."

Toyota spokesman Jim Wiseman could not be immediately reached for comment
this afternoon about the expanded federal review.

Since announcing its recalls and a production halt last week, Toyota has
maintained that problems with unintended acceleration were limited to floor
mat interference and sticky accelerator pedals.

Shinichi Sasaki, Toyota's vice president in charge of quality, today denied
accusations that electronic malfunctions were contributing to the reports of
unintended acceleration.

"We have not come across any case in which we have found a malfunction,"
Sasaki said in an interview in Japan. "But if any additional reports arise,
we will conduct testing using all technology at our disposal."

Also, in a full-page advertisement that ran in many U.S. newspapers today,
Toyota Motor Sales U.S.A. President Jim Lentz said: "We have launched a
comprehensive plan to permanently fix the vehicles we've recalled because in
rare instances, accelerator pedals can, over time, become slow to release or
get stuck. We know what's causing this and what we have to do to fix it."

But Safety Research & Strategies, a consulting firm, said in a posting on
its Web site: "Neither floor mats nor sticking accelerator pedals explain
many, many incidents" of unintended acceleration.






Read more:
http://www.autonews.com/apps/pbcs.dll/article?AID=/20100202/OEM01/100209971/1147#ixzz0eQGOJ5Z0

 

FWIW, one thing that aggravates stuck accelerator type problems in any
vehicle that powers the brake booster with engine vacuum (98+% of all
passenger vehicles) is that when the throttle is open much above the
idle position, the engine vacuum to the booster is almost nil, so once
the initial booster charge is depleted (typically happens with the 2nd
or 3rd stab of the brake pedal), the brakes are almost useless against
the pull of the engine.

You can see this for yourself in your own vehicle - with no other
traffic around and at cruising speed, simultaneously push on the brakes
and the accelerator - while still pushing the accelerator (you don't
have to push the accelerator very much to see this effect), release the
brakles and apply them again. You will be amazed at how ineffective the
brakes are. Again - it is not due to the engine being that more
powerful than the brakes normally are - it is due to the vacuum not
being available to re-charge the booster once the initial couple of
stabs at the brakes has occured.

 

http://a.abcnews.go.com/images/Blotter/ht_lentz_100202.pdf

Waxman: Toyota Told Us Gas Pedals Were Not the Problem

 

Yes, this is true. I had a manifold vacuum gauge on my '65 Dodge and
could watch the vacuum change depending on my speed and gas-pedal
behavior.

I thought there was some sort of design rule (if not gov't regulation)
that a car's brakes must be able to hold a car in-place regardless how
powerful the engine was. Presumably this test would be performed from a
stand-still. In these cases of run-away Toyota cars, it's
understandable that given a car that's already going 30 - 60 mph with an
engine running wide-open, that the brakes simply can't overpower the
inertia the car already has plus the power being delivered by the engine
(and combined with almost no vacuum boost assist).

A USA-today article from last week mentioned the mindset behind this
faulty computer-control situation is that the computer is programmed to
not judge what the driver's intentions are if it seems that both the gas
pedal and brakes are being applied at the same time. I think that's a
coward's way of explaining it.

One possible (but un-voiced) explanation is that someone has the patent
on having the computer reject the throttle-position sensor when the
brake is depressed (and it would cost a fortune to license it). Another
explanation is that it might result in a *lower* level of liability
against Toyota if it simply kept building cars with the same faulty
control pattern programmed into the computer instead of introducing a
fix for newer cars while leaving existing cars alone.

Today on the web I read an article showing in good detail exactly where
these pedals are sticking. It looks like 5 small teeth mesh with each
other (3 on the stationary fire-wall side, 2 on the moving pedal) and if
the pedal is pressed hard enough, these teeth end up sticking together.
The proposed fix is a metal bar that acts like a stop to prevent these
teeth from meshing to the point where they bind up. There appears to
already be a stop that's built into the mechanism, but it's smaller (and
shorter) than the proposed fix.

(I have no idea what the teeth are for - perhaps they are part of the
actual position sensor? Sensing electrical resistance as a function of
meshed area? Or perhaps optical?)

The article went on to explain that many German cars have the correct
computer programming (ie - brake over-rides the throttle sensor). Some
hi-end Jap cars might also have this. My theory is that if the car is
expensive enough to indicate that the owner has enough $$$ to sue in
case of injury, then the auto maker programs the brake over-ride
function into the computer.

There is one possible reason have the throttle pressed down while riding
the brakes - that's if you're stopped in traffic on a hill (facing up)
and you don't want to drift down and hit the guy behind you when you
take your foot off the brake. In that case, if you take one more sensor
measurement (vehicle speed as measured by the transmission output speed
sensor) then you can develop a set of rules as to when to over-ride the
throttle sensor and when not too.

 

In that situation, presumably you're starting from a stopped position,
you get a green light and you take your foot off the brake and shift it
to the gas pedal, where you come down but end up hitting both pedals.
Your brake lights blink for a split-second, but they'll still be red,
you won't advance very far (because your pressing on both pedals) and
the guy behind you won't get the impression that you're moving to the
extent that he's going to start moving and run into you.

 

My 2005 Subaru Forester had drive by wire. Never had a problem with
it, nor do I know of any similar problems in other Subie models.

 

Our 2002 Isuzu Trooper has this sort of system. I'm guessing it was
relatively new at the time as I recall seeing it mentioned as being a
"feature" or whatever. I've never heard any reports of problems with the
system... I'm guessing it was used in all the 98-02 models.

Interestingly enough, there was a recall on our 94 Trooper a few years back
for an issue with the throttle sticking - and it's a "traditional" throttle.

I think a lot of the new cars are indeed going with a "drive by wire"
system. I'm nearly positive that is how it works on the 05 Grand Marquis we
have as a company car at work...

Wesley

 

Drive by wire has to be just about standard here in the EU as emissions
are tightening every five years or so and ordinary injection whether
mechanical or electrical can't cope, so everything has to be controlled
by a pre-mapped microchip. It's not more unreliable than a straight
forward cable, remember the Ford Explorers with the sticking throttles,
which turned out to be a fault with the cruse control cable holding both
venturi of the carburettor fully open against the drivers wishes. (See
Youtube.)