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

I stand corrected! Yesterday, I posted that I wasn't able to induce an override while accelerating up a hill, depressing the brake pedal.

Today, I re-tried it, and yes, there is an override, like everyone has posted. One does have to depress the brake pedal a bit further than one usually needs to, though. My observation is that the Prius brake system is highly effective!

So, either that guy in California couldn't find the brake pedal, or there was a catastrophic electronics failure in his car.

I would like a recall...on my post from yesterday!

 

My 2010 Prius III is 60 miles old. My 99 Forester brakes were mush compared to the Prius brakes. I have not done the brake override test since so many others have, and tell me that it works. My husband keeps telling me not to brake so hard in the Prius although I feel like I barely touch them. I have no doubt that these brakes will stop the car under any and all conditions. Also, although the accelerator pedal is shaped differently and seems to be a little beyond the brake pedal at rest, the pedals have the same feel to my foot as far as resistance is concerned. I can see how the inattentive driver with the mind on other things could mash the accelerator thinking it is the brake, as the woman might have done who hit a wall recently.

 

Tom,

Thanks. We now have some data and a couple of points to be made:
1. There are at least two methods for the Prius (and probably other Toyotas) to detect that the brake pedal has been depressed:
a. Pressure sensors on the main hydraulic line.
b. At least one microswitch in the cabin, directly above the brake pedal.
2. In these forum there are at least two posts, and likely more, of Priuses with misadjusted microswitches on the brake pedal. In those two cases of which I am aware, the characteristics of the problem were:
a. The rear brake lights came on late after the pedal had been depressed some distance.
b. The microswitch in the cabin was adjusted too close to the brake pedal arm, apparently causing that microswitch to be always activated.
c. The same microswitch also canceled cruise control, which, likewise, would turn off late (after a bit of struggling with the engine).

All right: It makes all sorts of sense to have a backup sensor on brake activation. But, now you've got me going.

First: Every time I've read about that brake light adjustment, it's been one switch being adjusted. Hence, your statement about two microswitches being present means one of two things:
1. Both switches are in the same physical body above the pedal. (Doesn't sound right to me..)
2. The second switch is attached to a pressure sensor.

The duplicated pressure sensors you mention that detect brake pedal force don't quite sound like something that would light up a brake light or cancel cruise control; rather, they sound like analog pressure sensors whose outputs go to the brake computer and are used by the computer to control regen braking, ABS, regular brakes, etc. It might be that the computer sends a signal that turns on the brake lights and/or cancels the cruise control when it senses pressure on the brakes. That sounds too complex for me, especially if there's a duplicated pair of microswitches sending that information directly to the engine controller.

Next: Take those two microswitches. They can be set up in one of two ways:
1. Independent signals to the engine controller/brake lights.
2. Wired-in-parallel switches that use the same pair of wires to the engine controller/brake lights, the idea that if either switch activates, the same wires become activated.

I'm going to argue that, in the case of reliability, Toyota probably opted for #1 above. For one thing, if the brake pedal microswitch is always activated, software would notice no change when the pedal was pushed (note: Detecting changes is something that software can do, easily. It can also detect stuck-at-one, or stuck-at-zero faults, but only if somebody coded it in. DTC, anybody?). If the switches were wired in parallel, and the brake pedal switch was misadjusted too close, the brake pedal switch would cause the brake lights to always remain on, which isn't happening.

Hence: Why weren't these people with late-acting brake lights getting some kind of DTC?

Now comes the good stuff. It's software in the EC that does the brake override by killing the throttle. That software, if it's going to do brake override, has two signals to work with. I'll be my last slice of pizza that, during testing, the main signal they were testing against was the cabin microswitch. Are we looking at a software bug that only goes off if the microswitch is misadjusted?

OK: I know you people are out there. The stories I've heard so far on the misadjusted brakes were a combination of dealer-doesn't-think-anything-is-wrong/fixed-it-myself/dealer-fixed-it.

I want to hear more details. Did the late-lighting brake light show up as any kind of DTC? (It should have - the microswitch wasn't working! Or maybe the switches are in parallel, so it wouldn't be detected!)

This also suggests a method of testing this. Misadjust the brake pedal microswitch so it's always activated, then see if the brake override still works and everything else still works. This would be only for the brave of heart, by the way.

Comments?

KBeck.

 

I've never had the gas pedal stick but I've had my shoe bridge the gap between the brake and gas pedals. So when I pressed the brake my shoe also took the gas pedal down with it.

Its pretty unnerving because your instinct is to not let off the brake for fear of lurching forward, especially in close traffic. Which means you press harder on the brake but at the same time your increasing pressure to gas pedal.. very scary situation.

I've had it happen at least 3-4 times with my wife's 2008 prius.

 

And there's now a report that Sikes, Mr. Runaway Prius Owner, is 700K in debt and possibly behind on his Prius lease payments...

Oops.

KBeck

 

The two micro-switches are in one body. In other words, it is a two pole device. The two poles separate the brake light circuit from the CC cancel circuit.

The two pressure sensors in the hydraulic lines are analog and feed pedal pressure data to the brake ECU. This is used only to calculate the driver requested braking force.

Tom

 

I tried this today. My brakes engaged perfectly.

 

Greetings -

The smells are quite different (especially to people in the business) - although if it had a mechanical clutch, it would be difficult to differentiate.....

 

Geez, what size shoes do you wear!?

 

Don't tap the brake, press it. Your Prius will slow down without having to overpower the engine.

Tom

 

Press as hard as you need to slow down or stop. The engine will not provide power once you start braking. You can verify it by ear or by looking at the power display.

Tom

 

Absolutely agree
He certainly smelled it in his training days in driving track training, high speed pursuits with the breaks being constantly ridden. And, anyone following trucks downgrades would smell their breaks. Or, if in the past one of their own breaks dragged. Very distinctive indeed and never forget.

I also remember reading that the CHP saw the break lights being on.

 

My RPM didn't drop to idle when I tried this in the city but the break was effective at breaking. However, my car works just fine right now Hope I don't have to find out differently when the gremlins invade the system.

 

Engine RPM does not equate to moving the car in the case of a Prius. The Prius can run the engine at any speed while the car is at any speed. It's one of the beautiful things about an eCVT.

Tom

 

He wasn't driving a Prius. Chippie was driving a Lexus. Maybe he just pumped the brakes until they overheated & failed. If he had shifted into neutral he & his family wouldn't have died in the car.

 

Correct.

The ICE can still provide power to the HV battery, so you may see arrows going that way.

Tom

 

I seem to remember reading or hearing it on the news that the CHP checked his car and the break pads were almost totally consumed.

Depending on the micro switch, its arm may have some distance to move before it actuates, enough so that just by being in contact the the break pedal arm would not cause the light to be on, would be my estimation.