C1256/1391--anyone ever try using DOT4 brake fluid?

Perhaps you had a bit of grit stuck in a valve, and removing the accumulator allowed enough fluid to push it out when you powered up afterwards?

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Interesting findings.
There is a similar ABS Accumulator that fails in the Generation 2 Range Rover P38 which I own so I'm keen to learn more about the Toyota system. So....my take away is that a DOT 3 brake fluid refresh every 100K miles might prolong the life of the accumulator but still it seems these accumulators fail about 200K?

 

thank you so much! it works! i have a gen 3 2013 and the actuator was running every 35 seconds.

1- I disconnected the 12v battery

2- I pressed the brake several times to empty the accumulator.

3- I drained all the fluid from the tank

4- I added 1 bottle of dot 4 fluid

5- I connected the 12v battery

And at the same time the car was perfect! the brake pump no longer runs alone! it's like a new car!

greetings from Brazil to all friends of priuschat

@TMR-JWAP

 

Today after a few days with the dot4 the pump started to run every 1 minute sometimes.

How is your car today? put dot4 solved your problem? the pump turns on every how many seconds? Any DTC?

@TMR-JWAP

 

It is my hope that one day Prius owners will finally learn that the brake fluid must be routinely flushed and transmission fluid routinely changed as a part of preventative maintenance.

 

My Gen 2, 2009 Prius, 74,000 miles, has thrown the C1256-143 and C1391-591 codes. I cleared the codes, but expect them to return again after I drive the car a bit.

Very happy to have stumbled into this thread. As I wondered what I was hearing cycling over and over again wth the ignition ON, while connecting Techstream to pull DTCs. Sounds like a fluid pump cycling. The cycling never ends with the ignition on. So much cycling will lower the 12V battery voltage if I leave the ignition on for a period of time.
I now suspect I'm hearing the brake accumulator cycling. My Prius is relatively new to my ownership, so every DTC code requires another research effort. I'll time the pumping cycles, and see how it compares to the cycling times related in this thread. If it is cycling excessively and throwing these two codes, I'll try to mimic the process that TMR-JWAP used with some success. Cycle out the old brake fluid with fresh brake fluid.

I do have Techstream on a Windows 7 laptop computer. Is there a component of Techstream I can use to help confirm my cycling problem? I saw the ABS software tab within Techstream. Will the ABS software module provide data that will confirm what I now suspect is brake accumulator cycling? Can I see brake fluid pressure rising and falling real time, such as in an Active Test?

Any guidance/direction to help minimize my troubleshooting and diagnostic time will be appreciated! Links to other useful, informative, Forum Threads?

In the mean time, I'll further research the subject on this Forum, and see what I can learn about my Prius's ABS brake system.

I have a 2006 Toyota Prius Repair Manual, and I expect it will also have information on troubleshooting the ABS brake system, based on the below table I copied and pasted from it. Thought this Forum would be the best place to begin researching. Just getting starting on the troubleshooting...

 

If you are having pumping cycles that you notice as cycles at all, any efforts at timing them, etc., amount to little more than measuring the deadness of a corpse.

When the brake system is in good condition, if your foot is off the pedal, you can sit with the car on and finish a book without hearing the pump cycle. Even thinking about timing pump cycles means ... "it's dead, Jim."

 

Thanks for replies!

I suspect I'm hearing the pump cycle. My problem is, I haven't owned and used the vehicle a terrible lot, so the pump cycling is something I may have always heard, and just assumed it was normal. And it may now be bad enough to finally throw the two DTCs...

Relatively low mileage on the car. Someone mentioned this to be a common failure, but at odometer mileage much higher than my 74,000 miles.

I'll hook up Techstream and see if I can figure out how to run an active test in the ABS module that will show the varying voltages with those cycling sounds. If so, then I'll try the brake fluid flush. Brake fluid is relatively cheap!

 

Thanks for responding. As I stated in my prior post, it seems my Prius has always made some pump cycling sounds with the ignition ON. I probably assumed it was normal. Now that it's throwing these codes, and I've read this Thread, I expect what I'm hearing is this brake accumulator pump cycling over and over again.

Anyhow, once I gain sufficient comfort I have a correct diagnosis, I'll have to decide how to resolve/repair the problem...

 

It is normal for the pump to run occasionally, for a second or two, every few times you apply the brakes. You use up a little brake fluid from the accumulator each time you apply brakes, and after every few uses, it has to pump some back up. As long as you only ever hear that, it's normal.

If the pump is sitting there continually pumping things back up when you are not even doing anything to use up fluid, then in the big picture it really makes little difference whether it is doing that every minute, every ten seconds, or every two. Two is more dead than ten is more dead than sixty, but they all mean it has rung down the curtain and joined the choir invisible.

 

Good to know. Thanks. I'm a novice with this 2009 Prius.

 

If you have Techstream then why not? Open the ABS- VSC tab then go to data. Somewhere in the list is a line for accumulator pressure (displayed as a voltage of the pressure sensor). If I remember the pump kicks on when it drops to around 3.1V then turns off at 3.6V? And there should be something that says the pump (relay) was commanded on.

Posted via the PriusChat mobile app.

 

I just drove the Prius for a short 2 1/2 mile round trip. What I've been hearing continued to cycle even after I've shut the car/power button down. I hear the cycling for at least 60 seconds, maybe 2 minutes, after shutting down power to the Prius. Pumping sound for 5 seconds. Then no sound for ~6 seconds. Then repeats...
Is that normal??? Or is there another cycling type of sound that's normal on these Gen 2 Prius vehicles? I wouldn't expect the electronic ABS system to continue operations after the Power button is pushed off...

This short trip didn't trigger any warning lights on the dash display, so I presume the C1256 and C1391 DTCs weren't triggered.

 

The pump sounds a little bit like a rattlesnake. Nothing else under the hood sounds very much like it.

The brake system remains powered for about two minutes after you power the car off. It then does a little self-test dance before going to sleep.

Opening the driver's door wakes it up from sleep. Is the sound you hear then the same sound you're thinking of here? If so, you've identified it.

Not by any stretch of the imagination. Five seconds to pump, six seconds between pumps when you're not even using the brakes, that's positively awful. That pressure is leaking off nearly as fast as the pump can even replace it. When the system is tight you can read a book between pumps.

 

Thanks again. That pretty much confirms it's the brake accumulator pump. Between the 2 minutes of continued power to the brake system after powering down, and it being the same sound of cycling I hear when I open the door. Pretty much gotta be it.

I'll connect with Techstream, and should see voltage climb and fall with the cycling of the pump.

Then, gotta figure out the repair... Will probably try the brake fluid flush first. That will get me acquainted with the brake fluid system. If no improvement, then on to hard parts replacement... which sounds like quite a job.

 

I’ve been using the Motul Dot 4 or 5 I’ll have to go look at bottle my bike has same type pump accumulator type ABS as prii I own here. The ambers hav been on 2 yrs now but the brakes work wonderfully just no abs I can smoke up all 4 wheel wells evenly . So I keep driving I’ve 2 rebuilt accumulators sitting on floor.maybe soon wen gen 3 up n running

 

Does the rebuilding primarily involve replacing seals in the accumulator?

I'm researching the Forum now. Quite a number of brake actuator replacement Threads. Haven't found any Threads yet discussing rebuilds in their shop/garage.