Toyota Prius Forum banner
21 - 35 of 35 Posts

·
Registered
Joined
·
344 Posts
Dan-

I tried and tried but could not get my brake pedal to hit the floor.

Can you explain what's going on there? I've never heard of that happening before.

Thanks :)
 

·
Registered
Joined
·
344 Posts
i was trying to replicate what cattmatt had seen- sitting at a stoplight, firm pressure on brake, brake pedal hits floor.

i imagine he doesn't turn the car off at stoplights. why would the pedal hit the floor with the car on? that's what i'm wondering.
 

·
Registered
Joined
·
17 Posts
Discussion Starter · #24 ·
Buzz-3

I got my car back today and it's been fixed!

I am told that they replaced the brake system accumulator, and it was under & behind the inverter, thus the weeks ago service writer's thought that the buzzing was actually coming from the back of the inverter.

This incident seems to have been a first for them, perhaps both for the component going bad and for the sticky situation of a technician saying all is well and the customer saying "Sorry Doc, but I want a second opinion." (And being right.) I gather than the technician was brought to task and I imagine that there will be some discussion of what to do if/when this sort of situation arises again. Apparently there is a lot of paperwork to be filed on this issue. I'm just glad that I stood up for myself and didn't let a seeming authority override what my gut said was real.

And incidentally, after driving for a bit I got to a stop light and tried pressing firmly on the brake pedal again -- but the pedal is not as soft now, and it did not come close to depressing down to the floor. And after holding pressure for 10 or 15 seconds, I did hear the old buzzing for a short cycle, but that makes sense, having just put a strain on the system. That's the only time I noted hearing the buzz all day. So I have to figure that the pedal going to the floor was also a symptom of the system leak.

What a hassle! But what a relief!
 

·
Registered
Joined
·
7,161 Posts
There are 2 valves that are closed when the system is under normal operation, and that disconnects the master cylinder from the rest of the hydraulic system, except for the stroke simulator. If those stayed open, you would have an accumulator pressure leak, and would feel variations in pedal stroke.
 

·
Registered
Joined
·
4,873 Posts
I imagine that all the paper work is going around because it has been discovered that one of the two "failsafe" warning systems did not work on your car. When your accumulator failed, which caused the hydraulic pump (buzzing sound) to run continuously, you should have gotten a red brake warning light. ( One for accumulator failure, and one for hydraulic pump failure.) One half of the "fail-safe" brake warning system componants "failed." That would be great cause for concern. As an after thought, I tried to get my brake pedal to depress to the floorboards and it did not, "power on or power off."
On my other car with the old Bosch system with the power off it takes normally 32 pumps of the brake pedal to get "O" pressure and the pedal to the floor. The Prius system is much tighter and the accumulator along with several valves holds pressure with power off..........."ONE ADDITIONAL THOUGHT" ................ If it is found that it is a design wiring glitch in the present system that failed to give you the red brake warning light with the failure of your accumulator, every Prius made will probably be sent a mandatory "TSB". ........ If that happens, you have my thanks.
 

·
Registered
Joined
·
344 Posts
glad to hear you got it taken care of and the car is back to normal. the prius is still not very well understood by everyone and it sounds like the tech you had didn't want anything to do with yours. good on ya for standing up and making them pay attention to you.
 

·
Registered
Joined
·
7,161 Posts
But the accumulator was not running continuously. It did reach pressure and the pump would shut off. But due to a slow leak somewhere, the pressure would soon be lost and the pump would run again. The car is not programmed to determine the source of the loss, which could also be from actually using the brakes.

I suppose the car could meter how much brake fluid it released to apply the brakes, and within a certain margin could flag a problem if actual pressure loss did not match intended pressure loss.
 

·
Registered
Joined
·
17 Posts
Discussion Starter · #29 ·
Buzz-3

DanMan32 said:
But the accumulator was not running continuously. It did reach pressure and the pump would shut off. But due to a slow leak somewhere, the pressure would soon be lost and the pump would run again.
Right - it was not running continuously, but close. I think a slow leak was the problem, and maybe it was slow enough that it was just under the warning light threshold. Maybe. But when I tried to get the pedal to the floor again after the repair, after a bit the buzz did recur, briefly, and I interpreted it as needing to charge the system again after a heavy application.

I've done some errands here & there since and I've still not noticed the buzz again...
 

·
Registered
Joined
·
4,873 Posts
But the accumulator was not running continuously. It did reach pressure and the pump would shut off. But due to a slow leak somewhere, the pressure would soon be lost and the pump would run again. The car is not programmed to determine the source of the loss, which could also be from actually using the brakes.

I suppose the car could meter how much brake fluid it released to apply the brakes, and within a certain margin could flag a problem if actual pressure loss did not match intended pressure loss.


........U'm sure you did not mean the accumulator "not running continuously" The accumulator is a sealed vessel with a membrane separating a gas charge from a hyd fluid charge. The electric pump when temporarily running applys pressure in the accumulator which is stored and applied by the gas charge as the brakes are applied, eliminating the necessity of the pump to run continuously and wear itself out.
You should very rarely hear the hydraulic pump running. And any Prius mechanic that cannot determine that the hydraulic pump is operating is not a Prius mechanic.


................ ....... ................
 

·
Registered
Joined
·
344 Posts
i think Dan is trying to say that the problem wasn't enough to set a light because it was a slow leak and not a complete failure. the car couldn't determine whether the loss of pressure was coming from excessive braking demand or whether it was a leak.

now if something happened to the accumulator pump and it failed, that would set a brake warning light.

but your guess that all that paperwork was related to a 'fail safe mechanism failing' is questionable.
 

·
Registered
Joined
·
4,873 Posts
As a Prius owner and driver we are not supposed to personally determine that a componant in our brake system is malfunctioning. Catmatt recognised something strange happening to his car and Toyota maintanence didn't catch the problem as they felt if it was any brake componant failing (leaking) they would observe a red light warning. The gist of the problem was that catmatt recognised his hydraulic pump was running too darn long. Unlike an engine driven hydraulic pump the electric one in the Prius is not made to run continuously.
The problem here is that this type of system is probably not used in any other type Toyota car.
 

·
Registered
Joined
·
7,161 Posts
If the pump ran too long, then I am sure the system would have flagged a problem. But too frequent, it can't say is because of a leak, or because of proper but frequent use.

Try pumping your brakes 20 times, and see if the pump doesn't engage often. Then compare to press and hold.
One set of valves lets accumulator pressure flow to the wheel cylinders, another set of valves releases pressure from the wheel cylinders to the reservoir. If you use the brakes enough, the accumulator pressure would reduce as its volume decreased to the cylinders at each use. Eventually the accumulator pressure/volume has to, and is replenished by the pump.
Now figure that there is a slow leak anywhere in the system, but still keeping the system closed. That could be any of the wheel cylinder valves, the pump check valve, the accumulator over-pressure valve, or the master cylinder cutoff valves. The pump could achieve the needed pressure, since it pumps in much faster than the leak, thus proper pressure is achieved and the pump stops. But because of the slow leak, that pressure is not maintained, thus the pump has to replenish again, even though you did nothing to the brakes. A normally working system can hold the accumulator pressure quite a long time when the brakes are not being used. Since few of us hear the pump run when we open the door, yet a few do, I'd say the brake system can hold accumulator pressure indefinitely when no brake action is being taken.

The danger comes when the leak depletes pressure close to, or faster than the pump can maintain it. Taking 2 minutes to deplete the pressure to the normal low point where the pump kicks in is not what I would consider a serious short term problem, though usually such leaks will get worse over time.

But remember, even with complete accumulator pressure failure, the system will set the valves so that the master cylinders will have direct, but unassisted braking to the front wheels, and you have the mechanical braking with the parking/emergency brake to the rear wheels.
 

·
Registered
Joined
·
2 Posts
A buzzing noise occuring while you were talking sounds very much like the accumulator pump. That will operate a couple of times when off. So will the coolant storage pump operate briefly to be sure the thermos is holding the coolant temp properly.

From what I have heard, perhaps it was from Galaxy's husband through Galaxy, that it is your right to speak with the tech. I would complain to Toyota HQ that you were denied that right.
Actually, I have had that noise since the day I bought my Prius 11years ago. I did ask about it and they told me that was normal. I believed them, and have never had a problem since. Owned it over 11 years way over 100,00 miles with nothing wrong except the normal replacing the start battery and a couple change of tires. Oh, Imdid have one sticky caliper, but it was covered under warranty. It has been a wonderful car over the years. I’m getting tardy to buy a new one. Yes another Prius!
 

·
Registered
Joined
·
2 Posts
Actually, I have had that noise since the day I bought my Prius 11years ago. I did ask about it and they told me that was normal. I believed them, and have never had a problem since. Owned it over 11 years way over 100,00 miles with nothing wrong except the normal replacing the start battery and a couple change of tires. Oh, Imdid have one sticky caliper, but it was covered under warranty. It has been a wonderful car over the years. I’m getting tardy to buy a new one. Yes another Prius!
Sorry about the typos, I can’t find an edit button.
 
21 - 35 of 35 Posts
Top