Brake Accumulator failure C1391

My couple cents on this whole process.
Replaced actuator ("master cylinder" per junk yard) and accumulator ("Anti Lock Brake Parts ACTUATOR AND PUMP ASSEMBLY" per junk yard (I know, but this is how THEY are calling it)) over the weekends on my 2010 Toyota Prius with around 240k on a clock. Tried bugging Toyota about this repair, but I'm way outside the mileage and year on my car.
There are plenty of good instructions in this thread on how to do this as well as videos online, so I will just point out couple of my findings related to this process.
1. My 2010 Prius had Actuator part number 47210-47140(the mark that etched below TOYOTA sign). After some digging in documentation decided to take a risk and order actuator from 2011 Prius wit PN 47210-47310.
Per documentation this one is the successor of my original one, but ECU wise they should be the same. And it really did work, new unit didn't throw any code. Firmware wise, per Techstream my old one had F152647106 version and new one came with F152647109 version . Someone in previous posts mentioned 108 to be latest for 15" wheels, so got me worried at the beginning, but it did accept that software with no problem.
2. When installing actuator back in place, don't forget to put the spring that hooks to pin and helps to hold the pedal in upright position. You will have to play around it, cause the pin hole located right against steering wheel shaft, that will obstruct you from inserting it straight into place. I inserted it by depressing a pedal which gave me some extra room to shove the pin in place.
3. Bleeding brakes using Techstream and cheapo Mini VCI - just a nightmare. If there is any error code stored in ABS ECU - it constantly losing connection on a second step of "Bleeding After ABS Actuator replacement" process. To come around that, had to clear all codes in ABS unit, only then it let me through. But, it started randomly failing on Stroke simulator and accumulator bleeding steps (there are 6 cycles on acc bleeding process). I tried different battery maintainers, thinking that it might be battery power related, but nothing helped, it was just randomly failing. Only once it was able to finish 6 cycles on accumulator bleeding and failed on valve calibration preparation page (and that is where I gave up, thinking that if it came from same prius, previous calibration should fit just fine).
4. There is not much information about stroke simulator bleeding process online, so want to add couple words about it. If you will try to bleed it without Techstream or diagnostic tool - it wont work. When you get to Techstream step of stroke simulator bleeding you can hear a "click" in actuator, meaning that some internal valve is opened and only then you can play around by depressing pedal and opening stroke bleeder valve. Not sure if "invalid" mode will do the same, maybe some one can comment on that who used it for bleeding instead of scan tool.
5. When you are buying replacement part - better to ask junk yard to send you a picture of parts that they are planning to ship to you, cause with all that naming nonsense and their "don't give a sh**" attitude you might end up with lost time and bunch of unwanted parts. I ended up with extra brake fluid expansion tank with sticker "master cylinder" on it .
6. Places to order parts from:
- Ebay (lots of parts you need, but pretty expensive there nowadays)
- Car-part (probably the cheapest, but not many details online what car those parts are coming from)
- LKQ (Good info online, decent selection, price is moderate)
- Local junk yard (limited inventory, but if you are lucky - your best option)
- Toyota dealer (had to mention it, but if you are reading this thread - probably not your option)
7. Techstream - tried multiple versions. The most stable one for me was 12.20 (I believe it covers cars till 2018 production year) installed on 32 bit WinXP virtual box with xHorse 1.4.1 driver. Just look for "Toyota Techstream for ALL Windows" from Jafffa Adventures channel on Youtube, he gave pretty self-explanatory video on how to do the setup (kudos to him). With that setup Techstream worked fluently, except that bleeding process that I needed the most ((, but I don't think it was software issue.
8. Imho, bleeding process for me was way more tedious than replacing actuator/accumulator.
Actuator - easy-peasy, just make sure you tie up brake lines so they don't leak.
Accumulator - yeah, you will need to jump around it for a bit, but nothing horrible (took me around 1hr to swap it)
Bleeding with half working scan tool, empty actuator and accumulator from junk yard - painful.

 

Want to separate my question from the post above. After this tedious bleeding process that I went through, all codes are gone, accumulator holds the pressure steadily, no constant pumping and hissing from actuator. When driving - car brakes really good, better than it was before (no wonder, considering no one did brake flush on it for 240k miles), 60-70% pedal depress locks the wheels and activates ABS module (all I want to say it breaks really well).
But, when the car is parked or on a stop sign - I can easily depress brake pedal all the way to the "floor" without much resistance. I know it has stroke simulator instead of master cylinder with hydraulic pressure response like "normal" non-hybrid cars have, but with my old actuator the resistance was increasing proportionally as the pedal was getting close to the floor. In short words, even though my brakes works perfectly when driving, brake pedal feels "spongy" at rest. Did I leave some air in the system?

 

I think mine just feels that way too. If I think about it, I can press the pedal to its full travel.

I'm always hyperconscious of that right after doing a brake bleed, because I'm feeling for it and it makes me worry if I'm really done. But after some driving I eventually settle back down into "oh yeah, that's how it always felt and it stops fine."

Our system is really good at masking the feel of bubbles in the system, because it will just shoot more fluid in the lines and make the target pressure anyway. About the only time you can really feel for whether bubbles are there is if you drive with ECB disabled and see how it feels then. Maybe that's worth doing just for peace of mind.

There's a spot in the manual where it suggests a little trick for driving with ECB disabled. It's in a section testing for warped rotors (which ordinarily you can't feel through the pedal, again because of ECB). There's an ECB-Invalid mode, but it cancels itself if you start driving, so that's no use. They have you unplug the stroke sensor, which will create a trouble code and lock out ECB, and then you can drive and see what you feel.

 

I encountered the diagnostic trouble code C1391, along with various warning lights illuminated on my vehicle's dashboard. After researching online, I discovered that the culprit was a faulty actuator. I purchased a replacement actuator on eBay and successfully installed it. Subsequently, I utilized the Techstream tool to perform the bleeding process, ensuring proper functionality.

Following the actuator replacement, I have driven nearly 100 miles, and there are no longer any warning lights present. I confirmed this by using an OBD meter, which indicates that my vehicle is now ready for emission testing, with no pending trouble codes.

However, there is an unusual occurrence that I've noticed. When I press the brake pedal, I hear a humming sound. Additionally, when I start the car, this humming sound recurs at intervals of 5 to 10 seconds, repeating six to eight times. The same humming sound also occurs when I turn off the vehicle, again with six to eight repetitions and the 5 to 10-second interval. I verified that the sounds originate from the replacement actuator, and I can confirm that my brake pedal feels just as it did before the replacement. I have recorded a video of this phenomenon and uploaded it to YouTube, seeking input from the community to identify the cause of this issue.

 

Replied on your other thread.