Brake pedal to the floor?

When you walk to the car and put your hand on the handle, do you hear the brake accumulator pump run? It will be a faint whine. Just stand there without opening the door and see if you hear it.

If you don't hear it, you may want to take it back and ask the shop to check the brake accumulator pump operation. It almost sounds as if your car is not running it until you get in ...

Bob Wilson

 

I have to open the door to start it. It runs about 10-15 seconds, and is not at all faint inside my garage.

This is one of the noises noted in the Owner's Manual. If it is absent, definitely have the shop check it.

 

If your brake pedal goes to the floor with the car off, you need to have it checked right away for the sake of safety. Any car with power brakes must maintain braking action with the engine off, though the driver might have to push pretty hard for braking effects. Mine doesn't do this when starting.

 

I wanted to share that my 2010 also seems to have more "Pedal Travel" initially when applied at startup, but it definitely seems Normal in driving and other braking application. It may be a non issue but let's see if anyone else mentions it. I noticed it but didn't open a forum chat about it since from what I recall that's somewhat normal. But you should hear a sound soon after unlocking and opening your door. It's not LOUD but you should hear it when in a quiet enclosed garage.

 

Propose to keep a camera in the car. Next time you have the brake pedal to the floor then take a picture of it before you take your foot off the pedal.
Then take the car to the dealer and show them your picture.

 

The Hill Start Assist tied to the brake pedal gives it a different feel, IMHO.

 

I can't reproduce the problem. All I can suggest is a visit to a service center.

Bob Wilson

 

I think you are missing my point.
The picture is the evidence that the brake pedal goes down to the floor. It is because you are not likely to reproduce this when you bring your car to the dealer, nor any other Prius on the lot.
I believe the problem is unique to your Prius. With the picture you can insist the dealer to keep the car for couple of days and try to reproduce it.

 

I just went out to my car and the pump goes on when I open the door. I am able to press the pedal all the way to the floor (or a least to a hard stop which I assume is the floor) with little resistance. When I release, the pump comes on again for a few seconds. I never really noticed this before because I never smushed the pedal all the way down with the car off... I simply press it lightly and hit the power buttonm move into gear and I am off.

I am thinking this is normal operation. YMMV

Peter

 

I find the same thing while it sits in the garage. Will do more testing tomorrow with it On and Off.

 

I also think it's normal. Because of hillgrabber feature, there's a lot of travel in the pedal. I accidentally engaged the hillgrabber feature a couple of times when I first had the car, because I just kept pressing the pedal when I didn't feel total resistance. The pedal will go deep, and feels a little odd at first for that reason, but does need to go deep for normal operation.

 

When Prius brakes are operating normally, the brake pedal pushes only against a "stroke simulator", which is basically a piston on a spring. The stroke simulator doesn't harden up the same way normal brakes do. In other words, with normal brakes, as you push down you feel the brakes pressing against the disks or drums and the pedal gets hard. With the stroke simulator the pedal never does this until you get to the end of travel. It's a bit of a vague feeling.

In the event of power brake failure, the stroke simulator changes function and becomes a normal master cylinder, providing pressure for the front brakes.

Since this vagueness is subjective, we can't tell from the OP's description if this is normal operation or something else. I suggest comparing it to another Prius.

Tom

 

Good call! I'd read about it in the new car features but not really thought much about it. If it has become 'weak', the perception would be of the brake pedal going to the floor. But once the car is rolling, braking action would be normal.

To explain, when the braking function is in 'regeneration mode,' it is MG2 working as a generator, it is all electronic. The "stroke simulator" give the operator pressure feedback so it seems like a normal hydraulic brake even though regeneration is doing all of the work. In theory, a failed stroke simulator, one that is not providing enough resistance, would seem like the brake pedal was loose.

This should be something the toyota service center can quickly check but I have no idea of the repair effort.

Thanks!
Bob Wilson

 

Just curious - I certainly hear this sound and I read about the sound in the manual - but I don't really understand what an accumulator pump does (or is) and why it is associated with the braking system. ??

 

The brake accumulator pump and accumulator (a small, high pressure storage tank) provides the power assist when using the hydraulic brakes. In an ordinary car, the engine is assumed to always be running so their power assist units run off of a belt turning pump or in older cars, a vacuum from the manifold. This is why "Pulse and Glide" is considered so hazardous with non-hybrid cars as the power steering and brakes can become weak with the engine off. But our Prius was designed to often turn off the engine yet still drive just as before.

If all power were lost in a Prius at high speed, the accumulator tank would still have enough pressure the power assist on the brakes would still work. It is also the reason why brake work at home should be done very, very carefully. Even with the car off, there is high pressure hydraulic fluid in the accumulator. Bleeding could be ... exciting.

Bob Wilson

 

I suspect that if you pressed hard on the pedal when moving the pedal would have the same stroke except that the ABS would kick back at the pedal. When you're moving you only use light force on the pedal.