Brake Accumulator failure C1391

Good write up, I'm about to go down the same route. I just did a brake fluid flush using a Snapon Solus Ultra tablet which does the same bleed procedure as a Techstream. We'll see if I get the Christmas tree light dash again.

Since you got the same part number I'll assume that your original part was not part of the 2010 recall batch? Is there a way to check the part number of the part while it's still on the car?

 

Was there ever a 2010 actuator recall? Doesn't ring a bell with me. There was definitely an a accumulator recall, already mentioned upthread, but I've already flogged the horse enough about the actuator and accumulator being different parts. Prmp945's story is about an actuator.

There was an actuator firmware update for excessive honking/quacking. It's easy to use Techstream to check the firmware version currently running and compare to the updated number (which is different depending on whether you have 15 or 17 inch wheels). It can be updated without swapping any hardware.

I'm not saying there can't have been a recall too, that I just might not have heard about (or heard about and forgot)... do you have a recall campaign number for the one you're thinking of?

-Chap

 

I'm curious why the wheel size would matter on the update? I have a 2015 that came with 15" wheels that I upgraded to 17". The actuator started to make strange noises at 10000-15000 miles and eventually replaced under warranty

 

I did check the recall website with my VIN, and it did not say that my car was covered for anything.

You can definitely check the part number without removing anything - but it is quite difficult. You will need a flashlight to highlight the etched metal part number.

In the photos attached, I have progressively zoomed in on where you will find the part number. In the 3rd photo, you can barely make out "YO". This is an etched TOYOTA on the part. Look for this writing on your part with a flashlight and you will see the smaller part number etched next to it. Sorry, I could not photograph it installed in the car! The last photo is of my old defective part clearly showing the TOYOTA and adjacent part number.

 

Sorry I think the recall I am thinking of is the accumulator, not the actuator. Is the C1391 Abnormal Leak of ACC PRESS code usually related to replacement of the accumulator or the actuator?

 

Is this it, looks to have the special tools you mention:

https://static.nhtsa.gov/odi/rcl/2013/RCMN-13V235-0909.pdf

Which component is this?

My head is swimming with the names. Visual aid:



Apparently they replace our brake booster pump assembly, back in august 2013:



Still hearing an occasional odd noise when braking though. Maybe the "brake booster with master cylinder"?

 

One other thought from my experience: up until the repair, my brake fluid had never been replaced. It appeared clean and full. I had read discussion elsewhere on the forum about the fact that Toyota does not include brake fluid flushes on their maintenance schedule:

2010 Prius Maintenance Schedule (US) | PriusChat

I have to wonder if regular brake fluid flushes (i.e., 3 years) would have prevented this breakdown. It seems like it is possible that one of the valves inside the brake actuator got stuck slightly open due to grit or something. I know it is a "closed system" and grit getting in should not be possible. But isn't it possible that something inside the system deteriorated and created grit? I'm not an expert - I don't know!

 

Toyota Canada says (since maybe 2014) tri-yearly or 48K kms (30K miles) whichever comes first, for all their vehicles. There is a repair manual procedure for doing this without Techstream, and you should watch @NutzAboutBolts video, for hands on DIY procedure.

 

Iiiiixnaaaaaayy ... that's (once again) the recall for the ac·cum·u·la·tor, the one already mentioned upthread, with the special tools for replacing the ac·cum·u·la·tor. As it says right at the top:



The part replaced by prmp945 was the ac·tu·a·tor, the thing mounted on the firewall with the master cylinder and ECU built into it. Jkan2001 was asking about a recall on that, which I didn't remember.

Now that I'm home looking at my notes, there was also a recall on the 2010 ac·tu·a·tor, T-CP-A0B-0001-D, but it only involved a firmware update. That was the one to make the regen-to-ABS-on-potholes transition less noticeable. As long as your brake ECU has firmware F152647106 (for 15" wheels) or F152647126 (for 17") or later, it is up to date with that recall. (There was also a later version, F152647108 for 15" or F152647128 for 17", just to quiet the honks and quacks. That one was just a service bulletin, not a recall, so you pay for about an hour of shop time for the reflash if you want it done.)

I'm sorry to flog the horse more about getting the part names right, but they are similar enough that they really can be confusing for newbies. It's kind of on us as the regulars around here to be careful enough with our usage that the newbies at least have a fighting chance.

Yeah, there's the other set of equally or more confusing names. Repair manual and DTC descriptions tend to use actuator assy and accumulator assy; the part diagrams (different translation teams?) tend to use "booster with master cylinder assy" and "booster pump assy". Respectively.

... and if it seems like a full-time job getting people to keep actuator and accumulator straight, try getting them to remember there's a "booster" and a "booster pump" that are completely distinct parts, located in different assemblies, serving different purposes.

Maybe it is better just to remember:

THAT THING ON THE FIREWALL WITH A LOT OF TUBES AND WIRES AND THE BRAKE PEDAL PUSHING IN:

Contains:

1. The brake/skid ECU
2. The master cylinder (a pair of pistons you push with your foot to apply fluid pressure)
3. The "booster" (a hydraulic chamber behind the master cylinder pistons where high-pressure fluid can enter controlled by a "reaction disc" and valve in proportion to how hard you are pushing. The fluid pushes on the piston in the same direction, so it assists you. It is like the big round vacuum booster in other cars.)
4. The ABS ac·tu·a·tor, a lot of valves and pressure sensors that the ECU can use to modulate pressure independently at all four wheels for you so you don't lose traction.

THAT THING ON THE INNER FENDER WITH A COUPLE TUBES AND FAT WIRES AND TWIN ROUND CYLINDERS:

Contains:

1. The "booster pump", an electric motorized pump that forces fluid into the
2. ac·cum·u·la·tor, a nitrogen-filled pressure tank where the pressurized fluid accumulates until it is used (in the wheel cylinders by way of the ac·tu·a·tor and in the "booster" by way of the reaction disc) when you apply the brakes.

Clear as mud? And that's all just for Gen 3, other gens arranged the stuff differently.

The wheels have different radii, meaning different relationships between wheel speed and vehicle speed, and between brake torque and traction, and all of that is figured into the ABS and skid firmware calibration. Those aren't the only differences between (factory) 15" and 17" Prii; if you look up part numbers for the body sheet metal structural parts, there are a handful of differences, mostly around the hatch and rear wheelhouse areas IIRC. They are subtly different cars.

No easy answer. The code means what it says, but the leak in question could be in either unit. The accumulator is mechanically simpler, just a couple of valves (a check and a relief valve) and a pump, and the big accumulator chamber. The actuator has got nearly a dozen valves in it; in prmp945's case, sounds like it was a sticky valve in the ac·tu·a·tor through which the pressure in the ac·cum·u·la·tor was being lost. But that can also happen through a path in the accumulator itself. It takes a human devising tests and doing them and interpreting the results to decide which is at fault in any given case.

-Chap

 

Bravo, great post. I bled my brakes, drove the car for about 75 miles and the pump was still making a lot of noise and I got the Christmas tree lights of doom again. So now I need to figure out which part I need to replace and grab the part from Ebay.

I would tend to guess based on my reading here that the majority of the parts replacements (and the recall itself) are the accumulator not the actuator but right now I don't know if I fall into that group or not.

 

Hard to say. The actuator does contain about six times the number of valves to get possibly gunked up compared to the accumulator, which only has a couple. Accumulator pressure being lost through any path will of course set of the accumulator pressure loss code.

Techstream lets you watch the readings of all the pressure sensors in the system (I counted them once on the diagram; I think there were, like, seven), and it lets you toggle the valves individually open and closed. If the pressure drops fast enough for you to watch the numbers going down while you sit there not using the brakes, you might be able to play with some valves one by one, and see if you catch one that doesn't change the rate of pressure drop as much as the others, when you open and close it. That's a very preliminary idea; it would take close study of the diagram to flesh it out.

-Chap

 

Perhaps a dumb suggestion - but in my case, there was a "hissss" in between the pump noise. I am guessing this hiss was the leak. My ears placed the source of the noise at the ac·tu·a·tor rather than the ac·cum·u·la·tor. Low-tech, but maybe effective?

 

And a "mechanic's stethoscope", which, in its lowest-tech incarnation, can be a "long stick", is even better than unaided ears at pinning down where a sound is coming from.

-Chap

 

What sound would I be listening for? Right now it sounds like my pump is running frequently which means the accumulator isn't keeping the stored pressure right? Am I listening for a leak or something?

 

I do hear an occasional hiss noise but I don't know if that's normal? It's the same noise that I hear when I use the snapon tool to zero down the accumulator.

 

The hiss that I'm referring to is not a "normal" sound, but rather the incorrect leakage of fluid past an open/sticky valve in the actuator. It is fairly quiet because it is a small leak, not the same as the louder "zero down" sound. Now that I've replaced the actuator, I do not hear the hiss noise anymore, and consequently, do not hear the repeated (every 3-5 seconds) pump noise needed to restore correct pressure due to the leaky valve.

Note that I am making assumptions about what exactly the noises I have heard are attributed to, but I think the logic is solid.

 

I should add that your hiss sound could be louder than the one I heard if the leak is more serious, i.e., a valve is stuck more fully open rather than a small leak due to a bad seal.

 

I may just buy both parts and have my tech put them in, easier than trouble shooting.

 

@ChapmanF: since you seem to be the expert on this topic, what do you think about buying a newer (non-matching part number) actuator?

I purchased the same part number, but I wonder if it has the same weak point that let the original one die. If newer iterations of this part have improved design, obviously it would be better to use a newer part number. It sounds like this is possible to do, but requires reprogramming the brake/skid ECU (integrated into the accumulator unit) to match the car. Of course, if newer part numbers actually have the same design flaw, then it is simpler to just purchase a matching part number and not have to reprogram the accumulator's brake/skid ECU.

 

Related to my last post: do these failures occur less frequently on 2012+ models? It seems all the failures I read about are on 2010-2011 models. The answer to this question is important in determining if using a newer part number is a good idea.