Auto ECU's use the sensors to control fuel according to the voltage
   supplied by them. Most sensors output 1 to 5 volts. More volts is
   more fuel. The new drive by wire open the throttle according to
the   throttle position sensor.   That is also trimmed by the
traction and ESC controls built into the   software.    The O2
sensors are different in that they only operate on .1 to .9   volts.
  They generate this voltage in response to the O2 in the exhaust.
The   ECM is trying to maintain an A/F ratio of 14.7 to 1. This coincides
   with a voltage of 0.5. Diagnostics have an output of cross counts
   which is the number of times per second this voltage crosses the
   0.5V's. A high number (cross counts) is desireable for emission
   controls. As with other sensors, more fuel translates to higher
   voltage. The ECU then shortens the pulse width, (gives less fuel)
to   respond to the excess fuel in the exhaust. An O2 sensor that
has low   cross counts is due to be replaced. Fuel economy will
likely be   improved. O2 sensors SHOULD not have anything to do with
the   throttle position stepper motor. As with any man made device,
 anything can and probably will go wrong.    A few years ago, Audi
had a lot of trouble with the UNINTENDED   ACCELERATION PHENOMENOM.
One of the car magazines did some reasrch   and found the fault to
be small close pedals that low time (new   owners) mistook the gas
pedal for the brake pedal. In each incident   the owners were
positive they were stepping on the brake. The   magazine testers
were the same as the new owners that had their car   take off. ALL
CARS ARE DESIGNED WITH BRAKES THAT CAN HOLD THE CAR   BACK.
 Modified vehicles MAY be an exception.    In the expert witness
case, the driver could not have had their   foot on the brake pedal
firmly when they put the vehicle in reverse.   If it had been so the
vehicle may have moved slightly, but not   enough to kill anyone. IMHO.

   Dale Davies

   --
   Dale
    I can tell you from experience that the Audi problem was real.  I
   don't know what the problem was but it wasn't small close peddles.
   I had an Audi and experienced an uncommanded acceleration.  Here
is   what happened.  I turned a corner on a city street and started
to   accelerate and the car throttle body went "Wide OPEN"  the RPM went
   to about 6K.  I stood on the brakes and it was still accelerating
   and about to hit the car in front of me so I kicked the transmission
   into neutral and without a load the engine RPMs pegged for a split
   second and then dropped back down to idle.  I parked the car on
the   side of the road and called the local Audi dealer... Keep in
mind it   was "Not" under warrantee. They immediately picked it up,
 gave me a   free rental and fixed it for free.  Oh, this was the
4000S model and   not the 5000 model car that was suppose to have
the "Problem".  I   don't know what was wrong with it but I do know
it wasn't "peddles"

   Mike C.

Not necessarily calling bs, but I don't get it.  There's not a car
made that can accelerate as fast as it can decelerate.  That implies
that the brakes are able dissipate more energy than the engine can
deliver.  I believe the engine might have gone to WOT, but I have a
tough time understanding how the brakes wouldn't be capable of still
hauling the car to a stop.  One factor is that if the engine is at
WOT and you pump the brakes, the booster would quickly lose vacuum
and so you'd be without the brake assist. It might take a heavy foot
to get much braking effort, but the same braking power would be available.
And, I can imagine that it would be surprising as well..

Matt-

I have not tried it Matt but one can "fade" the brakes.
This is when the pad material gets so hot the coef. of friction goes
way down. It is a runaway situation. The longer you hold the pedal
down with full power the worse the brakes get. Also brakes boosters
work on vacuum. WOT vacuum is near atmospheric pressure.

Brake fade is very common in road racing. One of the first things
you need to do to convert a car to a road race car is upgrade the brakes.

Paul Lamar

--
I doubt my situation caused any brake fade as it was over in less
than 5 sec... I was on a 30 MPH zone and only about a car link and a
half from the car in front so by the time I stepped on the brake the
distance was closing very fast and I immediately went into
neutral... It was over very fast,... I remember starting to change
direction toward the curb to steer around the car as I threw it into
neutral... No Idea what caused it but it was real.  Not that the
following has anything to do with the "Audi issue" but for the Prius
problems... I personally think that there might be some EMI
issues... They certainly don't shield those cars or test them to the
level we do in Aerospace and I bet they have missed a corner EMI
condition... Which would explain the "Ghost" in the system.

Mike C.

In a road racing situation the brakes can fade in a fraction
of a second. You come into a 20 MPH corner at say 80 MPH (117 FPS)
and stand on the brakes.

The brakes can fade in 100 feet. Of course if you did not
brake then that cannot happen. That scenario is for those people
that tried to stop the car by applying the brakes.

Paul Lamar


Trying to back out of a parking stall and putting it in reverse says brake
fade was not an issue. Mike's problem could be different. A lot of heavy brake
use precedes brake fade. Three laps of the old Edmonton International Speedway
(remember that one Paul. I corner marshalled a few times when the
Chapparal was there) and my RX 3 had no brakes. 130 MPH into corner one. Yah
it can happen quickly, usually on a heavy car and a down hill. Drag racers
used to brake torque to warm the rear tires. Held the brake to the floor and
the gas pedal to the floor. They usually backed off the rear brakes a bit so
they did not hold as well. Then they could really melt the rear hides. The
front brakes still held the car back. I still say the brakes SHOULD hold the
car back. I could see some creep, but not the unimpeeded acceleration
described. If this did happen, the brakes should be really hot when the car
comes to a rest at the end of the event.

Dale Davies

I think the term unintended acceleration applies to a wide variety of situations.
I agree that from a dead stop the brakes should hold the average car from
moving as there is no real energy going into the brakes.
The lady in the parking lot could be faulted for not putting
her foot on the brakes when she selected reverse but how many
of us really do that all the time?

Paul Lamar