2010 Prius making a buzzing sound when depressing brake pedal and sometimes even when you do not

In a Gen 3, there are both of these things under the hood:



Either one can cause the symptoms you are describing. (Only the bottom one has the pump, but either one can be the reason the pump has to run).

So if one of those units was replaced and the pump still has to run frequently, then either (1) the replacement unit is faulty, or (2) there's a problem in the other unit.

The idea that the unit has to "adjust to the car" is pure woo.

 

itdepends on the scan tool. keep in mind, a brand new health brake booster makes a buzzing noise when you open the drivers door, and occasionally while driving. that's the pump pressurizing the system.
on my 2012 with 86k, it buzzes 10-12 seconds upon opening the door first thing in the morning. this is much longer than when new, but still operating well.

 

might be worth asking a dealer how much they want for a scan, aren't there any hybrid shoppes in LA?

if you paid the dealer for the initial assessment, ask the for the codes

 

It's a common misconception that the scanner tool can tell you what part is bad.

The scanner tools can show you the diagnostic codes the car's computers have set. But the car's computers can only set codes that say what the car's computers saw. The computers don't have any way of knowing why they saw what they saw, so the codes aren't going to tell you that. They just can't. That's the part for the human to figure out.

In the case of codes for the brake system, there are some codes that say "the fluid pressure couldn't be brought up to the right level" and some codes that say "power was sent to the pump for longer than should be necessary to bring the pressure up" and so on. Those are straight observations—the kind of things a computer in a car would be able to notice.

As to why the pressure is dropping, why the pump has to run so long, or whatever, some human needs to figure that out. There are possible causes in both of those units, and the car's computer or a scan tool by itself can't do that diagnostic gumshoe work for you.

Some mechanics will see that the description of a trouble code has the word pump in it, and then they'll say "the code said the pump was bad".

Unfortunately, that's a case of really not paying enough attention to what the code in fact means.

 

Did you get that situation fixed ?

 

Old thread, but facing the same problem, booster pump assembly replaced, but got the code C1391 after 60 miles.

 

You need to replace the brake booster assembly (the part above the booster pump assembly).