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Stability /traction control, Brake, ABS, ((!)) lights stay on C1391

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Ledorian, May 24, 2023.

  1. Ledorian

    Ledorian Junior Member

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    One day, I was driving my 2013 Toyota Prius Four through stop-and-go traffic at about 15 mph when I suddenly aggressively floored the breaks, slowing me down to about 5-8 mph. I did this to avoid a collision, but I ended up rear-ending a car. There was no damage to any cars and no one was hurt thankfully, but the impact felt quite aggressive, and it also caused my traction control, brake, ABS, and ((!)) light to turn on. I nervously drove away after exchanging insurance information , thinking my Prius breaks would fail...however it was driving and braking perfectly as it always had! so I kept driving it! 12k miles later I finally hook it up to my mini vci cable with Tech Stream to get rid of the codes. They were successfully removed, but once the lights are cleared, my car's breaking is funny? When I hit the brakes to come to a complete stop, my car starts to jerk and rock a little. But after about 30 miles, they all turn back on again and the smoothness of my car's breaking returns!!? The code "C1391 abnormal leak on accumulator" keeps coming up on tech stream even after I've cleared it out and driven it around a few times.


    The first thing I did was check the break fluid level. it was full on the line, indicating that there was no external break fluid leak, Phew!


    I'm considering simply replacing the brake fluid and bleeding the breaks to relieve some of the pressure my brake system possibly experienced during the time of impact, . Has anyone tried this? Would this work as a solution? I really want to avoid replacing any major components, like the break booster pump assembly (also known as the accumulator) and the break booster assembly.


    side note: I have replaced the brake pads in the past but have never changed the brake fluid or bled the brakes. Currently, my car has 169k miles.


    If anyone has encountered a similar problem with the code C1391 and fixed it, please let us know what you did!

    Thank you for reading I appreciate any guidance.
     
  2. ChapmanF

    ChapmanF Senior Member

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    There isn't any pressure in there to speak of that would be "relieved" by doing that. The accumulator is normally kept pressurized (at a pressure that doesn't depend on any impact) and the rest of the lines, etc., return fluid back to the reservoir and rest at atmospheric pressure when you're not braking.

    If you have a C1391, accumulator pressure is probably leaking down, which is what the code means. Do you have a scan tool you can use to watch the accumulator pressure reading?
     
  3. Ledorian

    Ledorian Junior Member

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    I appreciate you explaining to me how the accumulator works. I'm still learning a lot about this topic and your response is very helpful. I do, in fact, have Toyota Techstream, im using a mini vci cable bought off ebay.. What specifically am I looking for when looking for on the accumulator pressure reading? I can have someone drive the car and hit the breaks as I look at the laptop running the live tests.
     
  4. Tombukt2

    Tombukt2 Senior Member

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    I think you can just hit the brakes while you're sitting in the parking lot and see your pressures and do their thing and you can leave the car just sit there with the thing connected and see the pressure going down and then the pump coming on and the pressure going back up and this constantly repeats while you're not even touching the pedal which is the point of the whole exercise when the car is sitting nobody's touching the pedal car sitting there running everything ready ready for you to put in gear and back out of your parking space or whatever it is you're going to do but you do nothing Don't put your foot on the brake don't touch the gas don't even fiddle with the radio just sit there and look at text dream and the appropriate screen and you will see why you're getting the 1391 the pressure will go down and then you will see the pressure go up and you ought to hear your break pump ing the noise. And then this will just keep repeating itself which it should not be doing essentially.
     
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  5. ChapmanF

    ChapmanF Senior Member

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    Yes, if you have it graph the accumulator pressure, it'll be kind of sawtooth-shaped: slowly going down, until the pump cycles and bumps it back up, then slowly going down again, and so on.

    The key is it normally goes down really slowly. Sounds like yours isn't.
     
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  6. Ledorian

    Ledorian Junior Member

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    Thanks for the information!I'm going to run this test later today because my car always makes a hissing, pumping sound when I turn it off and when I gradually apply the breaks while driving. I know this sound originates from the brakes. The break fluid level at the reservoir is not at the full line anymore, which indicates that not all of the break fluid is returning to the reservoir right?. I'm considering filling the reservoir all the way to the top to see if that solves the issue, what do you thinkof that?
     
  7. Ledorian

    Ledorian Junior Member

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    I see! I haven't run the test yet, but I will do so very soon. Another thing I wanted to mention is that my car constantly hisses/pumps when I gradually apply the brakes while driving and when I turn the car off. I just checked the fluid reservoir level today, and it's no longer at the full line. Do you think filling it up to the line may solve this problem? I appreciate your advice so much.
     
  8. ChapmanF

    ChapmanF Senior Member

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    No. It has an internal leak, can't hold pressure. That's the hissing noise, and the reason the pump has to keep running to pump it back up. If you've already heard and noticed it doing that frequently, then there's no need to mess with a graph of the accumulator pressure to just show what you already plainly hear.
     
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  9. Ledorian

    Ledorian Junior Member

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    Gotcha , Thank you for the very useful information! So every 20 miles my car now switches the lights on and off? The odd thing is that the car drives and breaks perfectly when they are all turned on, but when they all turn off, the car starts to jerk and shake when I brake to a complete stop. This leads me to believe that perhaps the computer is acting up, so I may start by replacing all of the ABS fuses under the hood. we'll see what happens!
     
  10. ChapmanF

    ChapmanF Senior Member

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    If there are a bunch of lights coming on, there is more than one trouble code. (It may be that there is just one trouble code and other codes referring to it, but it is worth checking.) Would you be able to post all of the trouble codes you have the next time the lights come on?

    If you do not have a scan tool that will show them, you can retrieve the brake system trouble codes (any codes to do with the ((!)), ABS, or skiddy-car traction lights) this way:

    Blink (a/k/a Flash) Codes – How to. | PriusChat

    "My car seems to work better after the warnings come on, maybe the computer is crazy" is an idea people kind of routinely get around here. More likely it means the computer, once it detects failing stuff, switches to a fail-safe mode that works better than the failing stuff does.
     
  11. 2013priusguy

    2013priusguy Junior Member

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    @Ledorian did it work? This is a known problem and there were a bunch of TSB's on many Toyota and Lexus models going back to 2006. I don't know how they got away from a recall. The cost to change these is around $4k. I hit this issue on my Lexus and it is 115k. I don't know what to do. The current value or my car is around $5.5. I don't know whether I want to spend 4k to use the car for another 5 or so years. I am a Toyota / Lexus through out my life (5 cars) and I am VERY DISAPPOINTED with TOYOTA.

    Is there any other way to fix it without spending $4k?
     
  12. 2013priusguy

    2013priusguy Junior Member

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    I don't know whether this will fix the issue.
     
  13. Tombukt2

    Tombukt2 Senior Member

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    You shouldn't spend 4K to fix the brakes on this model The two parts together are only 1400 I think about seven a piece there may be even a rebuilt option or something if you scour the internet carefully getting used low mileage takeouts as possible from the JDM market there's ways to skin that cat If you want to spend 4K I guess you can If you want the new parts it'll be about 16 and then you can put them on or not.
     
  14. worldaven

    worldaven Member

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    Did you end up paying the $4K to fix the issue?
     
  15. Tombukt2

    Tombukt2 Senior Member

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    ours 2013 persona has never switched off once the brake lights come on they are on permanently VSC ABS traction control so on and so forth there's no intermittent about it not in the cars I've seen so far or owned rather once that lights on it's there even if I clear it with the scanner it's back within seconds minutes tops so if you've got codes going away completely disliding or unlighting the tree the Christmas tree that is you may have some other problem that could be a thing
     
  16. Tombukt2

    Tombukt2 Senior Member

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    ours 2013 persona has never switched off once the brake lights come on they are on permanently