More on that runaway Prius...

[Bob F]

Nonsense. Ballon Boy was just a innocent kid, doing what daddy told him.

Daddy? Maybe.

[Ed Pawlowski]

I think people know who I was referring to (except for you)

[Harry K]

???? Never heard of such a thing. I can turn off the key in every car I ever drove and it will keep on down the road until momentum runs out.

Harry K

[Harry K]

The Prius (and similar hybrids) are a whole different animal and I don't know much about them. There fore I usually don't comment on their specific controls.

The 'loose power and it stops the car' is too far out there though... I had to admire my 70 year old mother. She lost the water pump on a junker of a Mercury station wagon with power everything. I pushed her almost 20 miles including through a twon with 3 stop lights. In retrospect I should have paid for a tow.

Harry K

[bud--]

In any car with power brakes, if the power brakes fail and you push the pedal hard the brakes are applied by a simple mechanical-hydraulic system, just like before power brake assist was invented. If the power function fails, you still have the mechanical backup (but it takes a more pedal pressure).

It is inconceivable that Prius would not have that function as a backup on its brake system (which has a computer to control regeneration). My reading of post I responded to is that since Prius brakes are computer controlled, if you loose the computer you have no brakes.

Brakes are, of course, only applied when you push the pedal.

[clare]

The hydraulic brakes still work perfectly fine on a Prius if the computer quits or goes "APE"

[salty]

Unless they don't.

[Ed Pawlowski]

wrote

Could you give us a scenario where the computer will override the hydraulic system? Does something stop the master cylinder from making pressure?

[Bob F]

Antiskid brakes are the best example. The electronics release the brakes when the tire begins to skid. What happens when the electronics go crazy? Who knows?

[Ed Pawlowski]

"Bob F" wrote

Actually, a lot of people know. They default to plain hydraulic brakes.

[salty]

Something may interfere with the pressure getting to the wheels. This is especially true of cars with ABS.

[salty]

Unless they don't.

We are talking about a MALFUNCTION. Things often behave in unpredictable ways when they are malfunctioning.

[Ed Pawlowski]

You mean like an asteroid hitting the highway and bouncing up under the car. OK that could happen.

[clare]

When the electronics go crazy on antilock, you get manual braking. Might loose braking on first application, worst case.

Now, a MECHANICAL failure in the ABS CAN make your brakes totally ineffective. Had the gear fall off the brake modulator motor on my '95 Pontiac TranSport and it made the rear brakes totally inoperative.

[clare]

ABS only REDUCES the pressure when the wheels skid., Untill activated braking is normal.

[salty]

No, the results may be completely and totally UNPREDICTABLE. You can't state how they will work when they are not operating the way they were designed to operate normally.

Are you now claiming that 2009 Toyotas have 1995 Pontiac braking systems in them, or that 1995 Pontiacs have 2009 braking systems in them?

[salty]

Well, gee, Clare. What would happen if you were at highway speed and the computer malfunctioned and caused full accelleration along with reduced braking power? Maybe you just solved the mystery of why all these people are saying the brakes wouldn't stop the car even though they were "standing on the brakes".

[trader4]

And once again, that assumes the computer controlling the ABS is functioning normally. I thought the whole premise of the discussion was possible MALFUNCTIONS and whether they could affect operation. The ABS clearly has the ability to reduce the braking pressure to any wheel. By how much, I don't know, but I would suspect it would be a lot, as you might need to reduce it considerably to get a wheel to stop skidding. But worse case, if there was some bizarre bug that allowed it to happen, the computer likely could command reduced pressure on all 4 wheels continuously.

The probability that this is happening at the same time the engine computer is commanding full throttle would seem to be extremely low. Especially if they are run by two different computers. And it would likely also show up in the data stored on-board.

Just for the record, IMO the latest guy Sikes in San Diego is a lying skunk.

[clare]

Didn't say that, but unlike you, I DO know how ABS works. I know the failure modes.. I've likely forgotten more about cars than you will EVER know.

[clare]

YOU explain to me how anything that could/would cause the throttle to go to WOT could have any effect on the ABS sytem - specifically cause a false lockup detection - or how anthing that could/would cause a false lockup detection on the ABS could cause the throttle to go to WOT.

Or even how a REAL lockup detection could cause the throttle to go to WOT - or how a real WOT condition could cause a false lockup detection.

The only thing that can and WILL cause reduced braking power at WOT is improper use of the brake. The brake MUST be applied firmly and steadily to a stop. IF YOU PUMP (or release) THE BRAKE, you HAVE LOST BRAKING POWER. There is NO MANIFOLD VACUUM at WOT.