Chirping noise by the Brake pedal

That sounds like the noise of the power brake vacuum booster system (probably not the official name), and the chirping might be related to it since they occur together when you press the pedal. Normal cars use engine vacuum to provide power assist for the brake pedal, but the Prius Gen III uses a vacuum pump (the humming noise) instead. I would have my brake system inspected by a qualified mechanic. Others will be more qualified on the braking system and can explain it better.

 

Let's hope the diagnosis is correct, and you get back on the road.

 

In B mode there's less charging when braking. That's actually the main reason for that mode, to avoid overcharging on protracted downslopes.

 

If the Toyota service adviser says that there may be a leak in the brake booster, have them check for a safety recall notice. I have a Gen 3 Prius and I received a recall notice. Below is an exact quote from the notice:
Certain 2010 Model year Prius Vehicles Brake Booster Pump Assembly (Accumulator)
What is the condition? The subject vehicles are equipped with a Brake Booster Pump Assembly which can develop a crack inside the accumulator housing. If this occurs, nitrogen gas could leak into the brake fluid and gradually cause a loss of power assist. Under certain circumstances, this could affect stopping distance and increase the risk of a crash.
What will Toyota do? Any authorized Toyota dealer will perform an inspection and , if necessary, replace the Brake Booster Pump Assembly (Accumulator) at NO CHARGE to you.

 

I did more research on this and found that the Toyota recall is: D0H (that's zero in the middle). There is a Toyota video about this on you tube. Search for: "Toyota - D0H - Brake Booster Pump Assembly". You will see in the first part of the video that the labels on the accumulator are different between the bad and good ones. With a flashlight it is easily possible to see if the accumulator is the recalled one by just looking at the direction of the label. No tools required.
The video also explains that in some cases the whole brake booster assembly will need replacement along with the accumulator.
Something seems strange about this problem. I know that if a Toyota Service rep enters your VIN in the Toyota database, there is a red flag to indicate that this a critical recall. I'm sure that I don't have all the details about your problem so I'm sure that the best thing is to take it back to the dealer or maybe a different dealer to have them check if any part of your braking system is under recall.

 

I disagree. When our Gen II traction battery was old and would quickly swing from full to empty states, I became quite familiar with loss of regen braking when the traction battery got full on long downslopes. In this situation (regen disabled), all braking would be by friction, and B mode enables engine braking to assist the friction brakes. It is the control of the regen braking that prevents overcharging, not the B mode.

 

yiujai86 is absolutely correct. The exact same thing happened to me and I finally lost all power braking ability when the ABS, Traction Control, and brake warning light came on driving home from work last night. Manual braking remained, but just barely. Took the Toyota dealer almost 8 hours to diagnose the problem today and I got the same quote: $2800 for the part and about $700 for labor; $3500 total. I called Toyota about the recall because the symptoms, the lights, and the outcome were all the same. My Prius wasn't part of the recall, but I told Toyota maybe it should have been. That went over like a lead balloon and I got nowhere with them. Have to decide what I'm going to do. This may be the last Toyota product my family ever owns if we don't get this worked out somehow. If you own one like this, get rid of it before you get stuck with the bill and buy a decent car from someone else.

 

i'm trying to remember, did we have similar problems in the 2nd gen? IMHO, the brakes are a bit too complicated in the prius.

 

Sorry to revive an old thread but really looking for somebody to help.

2011 Prius. 100k miles.

Have had the same exact noise for a long time. Recently had the same exact brake/abs lights and braking issues. Took it to dealership. They replaced brake booster/actuator or something like that. The brake lights still intermittently came on. Now they’re saying that they get a code saying it’s the master cylinder. They want another $900 for that.

Is that actually what’s wrong? Or are they just taking expensive guesses?