Brake Accumulator failure C1391

Regrettably, I'm not an expert on any of those specific questions about interchangeability or unannounced improvements internally between parts.

As for a hissing sound, well, when you request zero-down in diagnostics, you're telling the actuator to open a valve and let all the fluid in the accumulator escape back to the reservoir. So yes, if you're hearing that same sound at other times when you're not telling it to do that, it could be your problem that you're hearing.

When do you hear it? There is an automated test a couple minutes after you turn the car off, involves a couple short hisses. That's normal; the whole test only lasts maybe five seconds.

-Chap

 

I believe I hear it when I'm holding down the brake pedal at a stop it sounds like it's non stop short hisses. It also does it sometimes while I'm on the brakes while slowing down. I need to find some time to diagnose which part to buy, the accumulator or the actuator

 

Maybe one of the SLR valves is not closing completely, the pressure sensor shows the pressure isn't holding where it's targeted while you hold down the brake, and the ECU is repeatedly goosing the corresponding SLA valve to keep the pressure up. Just a guess, from the way you describe it. Those valves are within the actuator.

-Chap

 

My car did the exact same thing while holding the brake pedal at a stop. It could be mitigated to some degree by just *barely* holding the brake enough to keep the car stopped. In any case, replacing the actuator fixed it.

 

Which one is that again? The more accessible one at the top, or the one further down, with twin cylinders? I'm never going to get this straight.

 

LOL, I'll save Chap a reply

Actuator = accessible at the top

 

Ok thanks! And the other one is accumulator. Actuator at top, accessible, Accumulator down low, total pain to access.

 

How about:

Actuator = actually accessible

Accumulator = access it later

 

And THAT, right there, is why I still believe that a tiny investment in learning what the system does beats all sorts of clever mnemonics for just memorizing stuff.

The actuator is called the actuator because it is how the ECU actuates the brakes. It needs to be the thing that has all the valves in it (at least two for each wheel, one to send pressurized fluid in, one to let it out, plus a few more for modulating and mode switching) and sensors, and a big nest of tubes coming out and going different places in the brake system.

The accumulator is called the accumulator because it does nothing but pump (that's one of the two big cylinders) brake fluid into a pressure can (the other big cylinder) where it serves as the source of pressurized fluid for the rest of the system. It only has enough wires to it to run a pump (and monitor it) and enough tubes to have a fluid gozinta and a fluid gozouta.

Think of all the clever mnemonics you want to just memorize some words, but if you just take the little time needed to have an interest in what the stuff actually does, you'll never confuse the words again.

-Chap

 

That helps me a lot.

 

Sorry, Chap. I didn't mean to belittle your helpful contributions on the matter, nor confuse anyone

 

Yep barely holding it (less than half travel) made it quiet. Still trying to find a decent independent tech to swap this part in DFW.

 

Actuator is the one they had the recall on for early 2010's that dealers usually quote 4k to replace right?

This stupid thing: 2010-2015 Toyota Prius ABS Brake Booster Pump Hydraulic Actuator Module | eBay

10 11 12 Prius Booster Pump 47070-47050 | eBay

 

Nope, that is the accumulator.

This is what the actuator looks like:

2010-2015 Toyota Prius Anti-Lock Brake ABS Pump Actuator 47270-47030 OEM A1 | eBay

There are lots of listings on ebay for the "actuator" that do not contain a photo of the item, but instead only show the crashed car that it came from. I would only purchase an item that clearly shows photos of the actuator, or else you may not get the part you are wanting. Apparently, the salvage sellers on eBay are just as confused on the terminology as people on the forum are (ChapmanF not included).

 

Have you considered doing the swap yourself? You'd save quite a bit of money, and it's not very hard. I'm not an expert by any means and it was annoying but pretty easy in hindsight.

You might consider doing just 1/2 the job: swap the defective actuator with a replacement yourself, and then pay a mechanic (with Techstream or similar) to flush the brake fluid for you and reset any codes. If you can turn a ratchet, you can do the swap portion of the job quite easily in an afternoon at most. If I had to do it again, I could probably do in 1 or 2 hours max. Flushing the brake system with Techstream was more challenging, but still within reach of any motivated person. If I had to do the brake fluid flush again, it would also take 1 or 2 hours max.

Doing this job motivated me to do a transaxle fluid replacement yesterday. Aside from a very tight fill plug, this job was easier than an oil change (no filter to replace). This cost me only the price of the fluid and a new crush washer (about $40 total). It's definitely good to learn how to do these things yourself. Lots of money to be saved, and more knowledge of how the car works to boot!

 

Quoting myself here to note that the seller states: "Altered from original condition. Missing components." Don't buy this one!!! But this is what the actuator looks like.

Are you going to replace your actuator with the exact same part number, or are you going to purchase a newer revision and have it reprogrammed for your car?

 

Are these happening to certain G3 Priuses? KNOCK ON WOOD..I have 160K and I don't have this issue...YET. But this sounds scary

 

I could be proven wrong, but from my reading it seems that the problem is almost always reported on 2010-2011 cars. Can anyone point to a forum post about someone with a 2012+ that reported this problem?

I first noticed a problem with my brake actuator at around 60,000 miles, and went down for the count about 5,000 miles later. With 160K, you've done a lot better than I did. Have you changed your brake fluid regularly, or ever? I don't think my fluid was changed until I replaced the actuator, and I have to wonder if early and regular changes would have prevented the problem.

 

There have been recalls issued for both items on early Gen 3s, the ac·cum·u·la·tor and the ac·tu·a·tor.

The accumulator recall only applied to certain early Gen 3s that got accumulators from a certain run (you could check either the VIN or the position of the label on the accumulator). That recall was an actual physical replacement.

The actuator recall was to make the regen-to-ABS-on-bumps transition less noticeable, and that was done with a new version firmware reflash, not a physical replacement.

There was later yet-another-firmware-update made available, just to quiet some honk/quack noises the actuator can make; that one isn't a recall, just an update you can ask for if your actuator makes those noises and annoys you; they may charge around an hour of shop time to flash it.

That's kind of a game-theory discussion that's been recently had again here in some other threads. We know that aged brake fluid can deteriorate, and that could lead to actuator issues. At the same time, we know the accumulator has a metal bellows sealing nitrogen into it, and a failure mode of that part is the fatigue life of the metal bellows (in fact, that failure mode is exactly what the accumulator recall was about), and the Techstream bleed procedure puts the accumulator bellows through at least six full-range-of-motion cycles in rapid succession.

So, folks on PC have been falling into about three camps on that:

1. Eagerly change fluid in order to best protect parts against corrosion
2. Leave the fluid alone and let sleeping accumulators lie
3. Use fluid test strips to judge actual condition of the fluid and consider (1) or (2) as indicated

I think I'm in the (3) camp myself, though I actually haven't obtained strips yet or done the test. An early PC member, hobbit, did and posted the results and mileage, suggesting it probably isn't an urgent test for me yet.

For anybody who does contemplate replacing either item (ac·cum·u·la·tor or ac·tu·a·tor) DIY, I would strongly suggest searching up the TSBs on techinfo that detail those replacements (or the instructions for the D0H accumulator recall). They give a bunch of cautions on procedure that I would not have thought of on my own, such as not using any textile fabric (no shop rags, no fabric gloves) during the work, as they can shed small fibers that aren't helpful in the actuator valves. These documents have more detail than just the sections in the repair manual.

For that matter, if you choose not to DIY, those are good pointers to make sure your chosen shop is aware of (and, if you buy used components, to try to find out if the dismantler was aware of).

-Chap

 

Brake fluid SHOULD be changed every two year. It absorbs moister because it is not a sealed system.
So a good flush is a must to keep the system clean.