I would really love some insight into this. So my Gen 3 Prius developed this issue about 6 months ago whereupon braking past regeneration it begins to make a sort of quacking/barking noise and there is some vibration in the brake pedal, though there isn't really any effect on braking performance. I took it to Toyota and they said it was an issue with the master cylinder and that it would have to be replaced for about $3k. Now I've seen the process done on YouTube and it seems like something that I could do myself with little issue, but I'm new to the hybrid and Prius life, and researching this has left me with questions on a few topics that I figure you fine folks may be able to educate me on: 1. On the Gen 3 the brake cylinder seems to go by multiple names when looking at the part for sale such as the actuator, accumulator, booster, etc. The terminology is unclear to me. If I'm understanding this correctly the cylinder is the part that is also called the actuator, and there is a separate part that has a different function that goes by the brake booster pump/accumulator. I'm just generally unclear of the separate parts and their exact functions and haven't been able to find any useful info on this topic. 2. Of these two separate parts (?) the cylinder is the easy one to replace, and the pump is a pain in the nice person that requires you to take the whole damn car apart to loosen a few screws holding in the seemingly accessible part. Is this correct? 3. As far as a proper diagnosis of the problem, does this noise indicate a cylinder failure from any anecdotal experience? Also, does this price point from the dealer seem to reflect a simple cylinder swap, or might there be more to the process such as the pump replacement? I can always take it back to the dealership for an opinion, and I may be cynical for thinking this, but could it be that they are trying to get me to buy into unnecessary services? I'll definitely be investing in techstream and a machine to run it as it will be needed in the bleeding process and it'll be helpful in future repairs down the line. Could that software help in diagnosing the correct problem? I feel like I have these general pieces of knowledge from the research I've done so far, but I just need help filling in the gaps and tying it all together. I'd like to become more proficient in hybrid and especially Prius repairs as I would love to make my car last by being able to take care of it myself and gain more knowledge of how it functions. Sorry if I come across as completely ignorant, a lot of these concepts are completely new to me and beyond my previous mechanical endeavors. And you never really know what you don't know! Before my Prius, I had an old Jeep liberty that was always having issues but the fix was always pretty straightforward. Thanks in advance for any knowledge you can share with me, it is truly appreciated!!
You're getting the terminology pretty much right. "booster", "master cylinder", "actuator", and "skid ECU" are all names the top thing will answer to. "booster pump" and "accumulator" are names the bottom thing will answer to. Be careful not to mix up the similar words "actuator" (top thing) and "accumulator" (bottom thing), or "booster" (top thing) and "booster pump" (bottom thing). Also, when you talk about a brake cylinder, it's important to specify which one you mean. The one connected to the brake pedal is the "master cylinder". There is also a wheel cylinder at each wheel. You should be able to find a decent amount of useful info on the topic by searching the site here. The go-to place to find diagrams like this one is the "New Car Features" manual, which you can read about here. All except the part about the master cylinder being easy to replace. It's a pretty decent pain in the nice person. It's just that the pump is worse. If you ever do need to do the pump, a great resource will be the video that Mr. F linked to just today, over here. The honking noise does come from the actuator (a/k/a booster, a/k/a master cylinder, ...). There are small valves in there that open and close, and sometimes brake fluid passing through one will honk it like a saxophone reed. You have a 2010, and there was a firmware update released for its skid ECU (also part of that master cylinder assembly) to make it honk less. This doesn't require replacing the assembly, just plugging in at the car's diagnostic port and flashing the update. I had my dealer do that and it reduced the honking. (It may change the way the ECU modulates those valves, like teaching the sax player better embouchure.) Even if you get Techstream on a laptop of your own, I would recommend going to the dealer for reflashes. If anything goes wrong during the reflash and bricks the ECU, you want that to be their problem and not yours. And they will be using a more reliable (expensive) J2534 dongle than you're probably going to buy for your own use. But you can totally use your own Techstream setup to connect to the skid ECU and find out its current firmware version, so you can see if maybe it is already the version they released to honk less. You find the versions on page 2 in T-SB-0363-10. If you have the 15 inch wheels, the dehonked version is F152647108, so if Techstream shows that version, then you already have the update. If it continues to honk with the dehonked software, the next thing I would try is a bleed procedure in Techstream, the longer procedure that would be used after replacing the actuator. It is possible there are bubbles of gas that shrink under pressure and expand when the pressure drops, and could cause unexpected spurts of fluid that honk the valves. If so, it may be quieter after getting those bubbles out. I probably wouldn't go to the trouble and expense to replace the thing unless the simple approaches didn't help, or it developed other symptoms or warning lights / trouble codes. PriusDadNoob, your profile says you have a 2007, which is a Gen 2. This thread is in the Gen 3 forum (tyty has a 2010) and the brake systems are very different. For example, Gen 2 has the pump and actuator combined into one assembly, instead of separate ones like Gen 3, but its master cylinder is a separate part, unlike Gen 3. If your profile is out of date and you really have a Gen 3, you can use the info in this thread, but if you have a Gen 2 it will be better to pose your question in the Gen 2 forum.
Wow this is an amazing post! @ChapmanF thank you so much. FYI I have replaced the actuator on my Gen 2 but recently bought a Gen 3 (2010) with a bad master cylinder assembly and pump assembly. That's why I'm interested in this thread. Thanks again, this is so informative.
@ChapmanF I took my 2010 to the dealer today for hard brakes. They don't stop the car as well at the bottom of pedal travel and are generally "stiff". No codes. They said it was the master cylinder assembly and pump assembly. I have not bled the brakes with Techstream, only with traditional bleeding. Do you think they are correct or should I get techstream (currently a Mac user!) and bleed before doing the replacement? I would just buy a used part from eBay I think as the new ones are $550 each.
You'll probably find Techstream very useful. Some people pick up an old beater Windows laptop to dedicate to the cause, and I've also heard of people running it on a Mac under virtualization. If you haven't bled the brakes using Techstream, you haven't bled them. "Traditional bleeding" of these systems is a fantasy; there are valves in there that aren't open unless Techstream tells them to be. Techstream can also let you look at a lot of live data from the brake system. If there are no warning lights and no trouble codes, one of the possibilities to look into here is maybe there's just a mismatch between how you expect the brakes to feel and how they do. In the Techstream active data list, you could log readings from the master cylinder and wheel cylinder pressure sensors for different amounts of force on the pedal, and we could compare those to another car.
When eBay shopping for booster pump assembly: there are two versions, same part no, but old (failure prone) ones have a yellow label applied to one of the cylinders longitudinally, while newer (internally revised) ones have the label transverse. Seems a bit of a “lapse” to me, that Toyota didn’t revise the part number. There was speculation here (by @ChapmanF ?) that it could be dealerships doing warranty replacements that were selling the removed (and defective) booster pumps. I might have mentioned all this in another thread you posted in; better twice than not at all I guess.
@ChapmanF Great advice. I just ordered an old Windows 7 laptop from eBay and an adapter from Amazon to get techstream set up. I have a Foxwell T630plus scanner that can do the bleed on my gen 2 Prius. It appears to follow the steps exactly like techstream. Pretty cool. But it does not work on my 2010 :-(
If you watch the video linked by Mr. F (see post #3 in this thread), it will show you how to recognize the recalled and good accumulators.
If you look in the attachment I posted, you’ll see it’s one of the good ones, at least judging by the label orientation.
I finally got time to work on my 2010 Prius and wanted to post a follow up. I ordered a USED replacement ABS module (the part the pedal connects to) and pressure accumulator (the cylindrical tanks). Paid around $200 each for these. I think the price has gone up with the cost of used cars skyrocketing. I replaced them and put a new gasket in between the ABS module and the firewall. I was faced with taking it to the dealer for the brake bleed or doing it myself and I like to do things myself. I had a ABS scanner that worked great to bleed my brakes on my 2007 but it did not work on this 2010. So I bought an old Windows laptop on eBay (that was a pain, so many junk laptops out there...) and a Tech Stream cable and software. After a lot of trial and error I did get the bleed procedure to work and my car is now stopping great again! One point, I did have to adjust the brake light switch to keep it from coming on when parked. I just twisted the green part of it and pushed it in and out until it was off when the pedal was fully up. Thanks again for all the help everyone.
Are you certain you got the replacement actuator completely seated down flat on the firewall? The adjustment you needed for the brake light switch makes me think the pedal might not be coming back when released quite as far as it used to.
To be clear though the gen 3 is the one that you can't buy the parts for new only JDM or junkyard is this correct I know it is for the gen too but i'm thinking the gen 3 is now this way too??
Gen 3 has two different thingies: I looked on parts.toyota.com just now and both are shown with normal prices and nothing about availability problems.
