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