buzzing noise upon braking from lower left area under dash

RE: 2011 Prius. I just wanted to put this info in here, in case it would help someone else. So far it has saved me over $2,100, which is what my Toyota dealer quoted to replace the accumulator pump along with a couple other items. I have had the car over 4 years with no problems...love the thing, but about 8 months ago it started making these wierd buzz-like short term noise when I stepped on the brake. It got pretty bad, doing it several times when I would be at a light or stop with my foot on the brake for a couple minutes. Long story short, I talked to Toyota and a Prius specialty repair shop. Both said it was the accumulator pump, the master cylinder and I can't remember the other item, but these parts would be replaced along with the accumulator pump. Here's what worked: I sucked out all of the brake fluid from it's reservoir (master fluid), as much as I could with a new turkey baster and smaller ear syringe and replaced it with brand new (unopened) brake fluid, filling to the max line. It cured the noise in a couple miles on my test drive (about 4 months ago) and then the noise started again recently. I went and bought another canister of new brake fluid and did this procedure again, praying it would work. It did. I live in Florida a few miles from the ocean... humidity galore ...and I can only assume there is some contamination getting into my system...someway. I don't have a clue but I'm thinking maybe a vacuum leak?? I do know brake fluid has the ability to pick up moisture, making it....bad. So, if you have some in your garage...don't use that if you want to try this. Buy new. That's my story...and it's true. Hope it works for you. The Prius shop said it wouldn't work and had nothing to do with my problem. WRONG, at least so far.

 

No codes or other indications of a problem. In response to the other replies, there are lots of noises in a prius that one gets accustom to. This was a new noise, and rather irritating. Also, I took the car to my prius specialist (he has a lot where he sells nothing but prius' and also does some mechanical for his customers. He listened to the noise and told me it was the accumulator pump. He is also the one though, who told me changing the brake fluid wouldn't change anything. I was cautious not to jump to conclusions after the first brake fluid change (because I was so hopeful it would help), but it obviously took care of the noise. Then as I had previously discussed, it did come back in a few months and I did the same deal again...worked again. Maybe my discription of the noise as a "buzz" isn't very accurate, but I can assure you it's not a normal noise for my car. In fact, that was demonstrated by the fact it was getting worse with just about each stop. With regard to the noise, if you would choke a duck, he might put out this short (1 second) objection!

 

Pretty sure the 12V battery is good. Since it's not making the noise anymore, I'm just going to ride it out. If it starts again, I will probably change the brake fluid again to resolve. Although, getting the codes read seems like a good idea. I stay as far away from the dealers as possible...can an autoparts store read the codes...do you know? I'm not positive how to navigate this site, so forgive me please if I screw up. Based on history, very likely!

 

Thanks much. I am afraid to try this due to my lack of electrical knowledge...car mechanics knowledge in general...but I did watch the video and wanted to mention to you that my ABS break light is not on. The noise I was hearing has indeed started to come back also, so I guess it's another break fluid change for me. Let me ask you this. Is it possible in your knowledge, that I could have a vacuum leak allowing moisture to enter my breakline system, causing the breakfluid to get contaminated. Thank you for your input...I appreciate it for sure.