buzzing sound during braking (sometimes)

[zeeman]

sometimes when i step on the brake there is a buzzing sound that stays on for a few seconds on, then it goes away.
it sounds either like electro-mechanical actuator or some solenoids that are pulsing a few times per second.

I am guessing that this could be the noise from solenoids in braking system, but i am not sure.

i only noticed that this noise sometimes happens when brake is depressed.

what is it?

[Patrick Wong]

This is the brake pressure accumulator pump. If you repeatedly pump the brake pedal, you will force the pump to run.

The sound is normal.

"Normal" cars do not have this pump, as they depend upon engine vacuum to create brake power assist. Since the Prius gasoline engine frequently is not running, engine vacuum cannot be counted upon to always be available. Hence Prius has an electric motor that intermittently runs this pump to build up hydraulic pressure so that when you depress the brake pedal, the car will stop.

[zeeman]

Originally Posted by Patrick Wong

This is the brake pressure accumulator pump. If you repeatedly pump the brake pedal, you will force the pump to run.

The sound is normal.

"Normal" cars do not have this pump, as they depend upon engine vacuum to create brake power assist. Since the Prius gasoline engine frequently is not running, engine vacuum cannot be counted upon to always be available. Hence Prius has an electric motor that intermittently runs this pump to build up hydraulic pressure so that when you depress the brake pedal, the car will stop.

oh, that makes sense.
this electrically driven pump probably presurises the brake accumulator, so that there is reserve capacity for a few full stops.
I presume accumulator is typical "bomb" type that has steel diaphragm and nitrogen on one side and hydraulic line on other side.

I am guessing that this is similar system to Citroen that (I think) pioneered this kind of accumulator, except Citroen used a pump attached to the engine whilst prius is using electrically driven pump.
is that about right?



thanks for the answer!

[toytech]

you should have that inspected by your toyota dealer there are tsbs for abs actuator noise its a very expensive repair if your vehicle is out of warranty..yes there are some normal operational sounds but your dealer technicial will let you know

[qbee42]

Originally Posted by toytech

you should have that inspected by your toyota dealer there are tsbs for abs actuator noise its a very expensive repair if your vehicle is out of warranty..yes there are some normal operational sounds but your dealer technicial will let you know

If it's just a little buzzing sound there is no need for a trip to the dealer - completely normal.

Tom

[Stefx]

Mine does that as well. Don't worry. Perfectly normal.

[qbee42]

Originally Posted by Stefx

Mine does that as well.

They all do it. Some people can hear it, some not, but they all make that sound.

Tom