How can there be ANY runaway Prius'es if they have brake override?

Umm.. OK, so I took a Dodge Caravan up to the top of Mt. Washington in New Hampshire and back down again. On the down side, had to stop because of Smoking Brakes. They sure do smell funny, distinctive, and all that other good stuff.

Officers in squad cars do accident investigations for a living. While I'm sure there's a fair number of accidents where the brakes never got touched, I'll bet there's a healthy percentage where there's hundreds of feet of black marks on the road with a car with smoking brakes at the end of it.

Finally, CHP cops aren't just hired off the street, given a uniform, and sent out on patrol. The word is that they get extensive training. Wanna take bets they get introduced to burning brakes when they do?

KBeck

 

Interesting. Later in this thread there's a video of a Prius where the brake override definitely did work.

OK. I'm not arguing with the people who think that this guy, Sikes, might have set this up. But I got a strange idea. I'd like somebody to speak up and say that it's full of garbage.

There's been several threads recently stating that the brake light/cruise control cancel/what-all switch, next to the brake pedal, has been misadjusted on several Priuses. I was surprised, somewhat, by one of the descriptions of both the fault and the adjustment; specifically, the author of that post said that there was no clearance between the switch contact and the brake pedal lever arm, when there was supposed to be some small number (2 mm?) between the two.

I've never adjusted the switch on a Prius, but I have done it on a VW beetle and a couple of different Hondas over the years. On all those cars there was some clearance to start with; had there been no clearance, the brake light would have been on all the time. The cars being discussed here were straight hydraulic brakes, no ABS, and, in the Beetle's case, no power brakes, either.

Now I'm wondering. There's more than one way to sense brake activation, especially since there's this fancy computer in the Prius and probably a bunch of other Toyotas. Might it be that the Prius (and maybe other models) notices that the brake switch is on all the time, figures that the brake switch is faulty, and switches to an alternate way of sensing brake activation? I wonder if the software running around that particular software path is as fully tested as the rest?

Comments?

KBeck

 

Ryung, if you're ONE car length off *my* six you're going
to get told in no uncertain terms to BACK OFF. That's not nearly
far enough.
.
Three seconds, minimum. I learned yesterday that the Smith System
which trains a lot of truckers is now calling for four, which
is nice to see.
.
_H*

 

I agree 100%

 

I notice that practically no one has answered the OP's very valid question.

According to most posters on this thread, all reported instances of run-away Priuses did not occur. They state that accelerations were faked, or some other opinions. The brake override is acitvated by 12V from the brake light switch, as is the cruise control cancel function. If the trooper saw the brake lights, the brake pedal had to depressed enough to activate the switch and, therefore the override.

The OP had a valid question, let's give him the respect of an answer, not a lot of conjectures or far-out scenarios.

Was the override defective on this Prius and other reported run-away Prii that have been reported for some months, or not? You can't have it both ways!

 

Not necessarily his conscious fault. Munchausen syndrome, applied unconsciously to an automobile. I mentioned this in another post. I believe it's the most logical explanation.

 

By the time the cops were to get to the accident, the smell would be long gone.
Besides, the point I'm making is that in court that is exactly what would be said and anybody listening is going to say 'Thats right, he isn't a mechanic'.
It's been done many times and it works.

 

It could be that they added it during the SW update then or, maybe none of us 3G's really have it. After all, that video is of a GII so who knows for sure.
OTOH, maybe the disable works off the brake lights and we know the Prius B-lights don't activate until the pedal is pushed fairly hard.

 

If you have to push your brake pedal fairly hard to activate the brake lights, your brake light switch is mis-adjusted and needs to be adjusted so that the lights activate at the proper position of the pedal position, approx. 1 cm of movement, see maint. manual for exact specs.

 

I agree, something smells funny about this, and I don't mean the brakes.

After a short time of this high-power run, I would think the traction battery would be depleted and the Prius would then have nothing left but the wimpy 70 hp atkinson cycle engine. Usually, this gets electric assist when a surge of power is needed, but I would think some minutes into this high speed, brakes on adventure, battery power would be gone.

Forgetting all this about brake override for a minute, is it really possible for the Prius to reach 94 MPH, with the brakes on, with nothing but 70 hp from the gas engine?

I'm sorry, but I suspect fraud here. Could be some guy who hopes to make a killing with a lawsuit (the lawyers are already circling Toyota). Could be some publicity seeker like balloon boy's dad. Too often, once someone has a defective product claim, certain dishonest individuals try to fake the same problem hoping to collect. This all is reminding me of the syringe in the Pepsi incident from years ago (if you never heard of this, Google "needle in pepsi can").

 

For the Gen II (this may be different for the Gen III):

Brake activation is sensed by two independent pressure sensors on the hydraulic line from the master cylinder. These sense how much pressure the driver is applying to the brake pedal.

Two micro-switches are used to tell that the brake lever has been depressed. These two switches control the brake lights and the CC cancel.

In addition, a potentiometer measures the position of the brake lever. This potentiometer is used to measure the rate at which the brake pedal is pushed. Fast brake pedal application is one of the two signals used to initiate Brake Assist.

Only the pressure sensors are required for working brakes. Lacking that the brakes revert to manual mode.

Tom

 

A prius can turn three digits with 30 - 35 kW worth of engine.
.
_H*

 

I had almost the same experience downhill on Pike's Peak in a 70s Ford LTD in 1981. The difference was I was pulled over by a ranger who pointed out the smoking brakes and probably saved me and my passenger from going over the edge. Once out of the car, it was a distinctive smell that I think I could identify today.

I would not be surprised if similar acts of stupidity are regularly witnessed by CHP, so I'm inclined (pun intended) to believe the cop when he says he smelled burning brakes. An examination of the vehicle will shine some more light on this.

 

Assuming that this is the case, what would happen if there was a bad connection on the line between the the brake switch and the module that cancels cruise control?

 

You hit the off button?

 

Manual braking would override the CC.

Tom

 

3. The driver did not press the brake pedal hard enough to engage Brake Assist, but instead just braked lightly.

I think this might have been the case with the driver in San Diego.

I think this is the key; try again but hit the brakes more firmly and quickly. You should invoke the Brake Assist and the car should stop quickly...Do this away from other traffic and make sure there aren't any loose objects in the cabin. :madgrin:

See this thread for a Toyota demo:

http://priuschat.com/forums/prius-h...t-screen-braking-demo-toyota-canada-demo.html

 

According to the drivers own words I saw on a tv show, the officer told him to use the emergency brake, he said the car immediately slowed to 50mph. According to their "computer generated simulation" they showed, the car pretty much stopped on its own and he pulled in front of it. I thought he couldn't have done too much stopping with the police car because it looked like there was no damage to either.

the driver was going for over 30 miles!!!! Of course there is going to be burning brake smells, he obviously was trying to stop, but the more you slightly press the brakes, the more they heat up and the less they do.

 

I commute 40 miles each way to work in stop and go traffic. Every day I have to suddenly brake from 65 miles an hour down to 30 or even a full stop. It seems pretty obvious to me that this man was definitely pressing his brake pedal and the car wasn't stopping. Forget about 30 miles... if that happens to me once for just 100 feet, I'll probably rear-end somebody on the way to work.

I'm just about to buy a new car, and Prius is the most sensible choice, except, of course, for this. I can't decide what to do.

 

Now is the perfect time to buy a Prius. All this is nothing more than a media storm and hysteria. You should be able to get a good deal right now.

Tom