How screwed am I? Brakes don't work.

Discussion in 'Gen 2 Prius Technical Discussion' started by priusmanneedhelp, Apr 28, 2022.

  1. priusmanneedhelp

    priusmanneedhelp Junior Member

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    Got in my car the other day and saw the BRAKE, ABS, AND (!) lights on. When I go to put in to gear the brake pedal sinks to the floor. Doesn't leak fluid though. I connected to techstream and got the codes in the Pic. How do I narrow down the issue? abs codes.png abs codes.png
     
  2. Tombukt2

    Tombukt2 Senior Member

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    Looks to me it looks to me like the first code you got us to check the 12 volt for abnormally low or high voltage probably where i'd start just because everything in the prius has something to do with some kind of voltage low or high voltage I have the same problem in one of my priuses but my brakes work all the time the VSC amber's the brake red and all those lights are on not the red triangle of death or the amber triangle of death depending on the year I have no anti-lock I have regular corolla four wheel brakes two wheel front disc two wheel rear drum and if I press hard enough on the pedal I can smoke all four wheel wells but the car stops very well thank you it's an internal leak of some sort in my case parts not available technically
     
  3. priusmanneedhelp

    priusmanneedhelp Junior Member

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    Got a new 12v after this issue started. Still remained.
     
  4. Tombukt2

    Tombukt2 Senior Member

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    Then it sounds like you've got such an internal leak you can't make any pressure usually what i've noticed in the two cars that i've had this go bad on the pedal is so hard to push you're stopping like a flintstones vehicle two feet on the ground two feet on the pedal back against the seat back pushing with all your might and stopping just before you hit the object in front of you it'll scare regular person to death i've never seen one where the pedal goes to the floor trying to activate the brakes that's like an old corolla with a massive fluid leak that you can see on the ground or on a wheel on a specific wheel usually that's when the pedal slips right to the floor so not had that in any of my prii yet
     
  5. mr_guy_mann

    mr_guy_mann Senior Member

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    Click on the snowflake symbol next to the C1241- that's freezeframe data. It will give details about when it set the code as well as a sub or INF code. This code is primarily about a low/missing (or possibly too high) 12V circuit for the ABS system. The INF code will give you specifics as to what is missing. Loss of power to ABS could explain (almost) everything else.

    Likely will need the service manual and a wiring diagram.

    Also, if the brake pedal "sinks" when the system is in failsafe- then you likely have air trapped in the hydraulics. Most people report a hard pedal when a Gen2 is in failsafe. Once you fix the electrical fault you'll want to bleed the brakes.

    Posted via the PriusChat mobile app.
     
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  6. priusmanneedhelp

    priusmanneedhelp Junior Member

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    Is it possible that if the abs isn't getting the correct voltage that it would cause the brakes to not get pressurized aka mushy?
     
  7. mr_guy_mann

    mr_guy_mann Senior Member

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    Possibly- just going from other forum members descriptions of pedal feel in fail-safe. Never heard anyone call it "mushyx. Usually say the pedal is hard like it lost boist.

    Normally the brake pedal master cylinder is connected to a "stroke simulator" that mimics brake feel on a normal car. Pressure and pedal position sensors allow the Hybrid Control ecu to figure out how fast you want to slow down.

    Then the HC ecu decides how much regeneration vs hydraulic braking it needs to do, and passes on commands to the ABS ecu. The ABS uses a pump to pressurize brake fluid, an accumulator to store the fluid, and valves to apply fluid to the brakes at the wheels.

    So most of the time your foot is never directly "connected to" the wheels. There can be some air in the ABS plumbing, and you wouldn't notice it. Up to a point the ABS ecu just opens some valves a little more to get things done. If it takes too long for pressure to build in some part of the system (ie, too much air that has to be compressed) then the ecu will set a code.

    The ABS system is designed to try and maintain as much braking function as possible in the event that something fails. The last level of this is where the master cylinder is directly connected to the front calipers- no electronics, pump, or anything to assist or affect braking.

    If there had been some air in the system, now the master cylinder has to use some if its volume to compress that air before pressure can increase and the calipers apply.

    Posted via the PriusChat mobile app.
     
  8. priusmanneedhelp

    priusmanneedhelp Junior Member

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    got some new info. So I reconnected to my car and clicked on the snowflake for the low voltage code(results in pic) and for funsies I cleared the dtc and the code is gone along with the changeover solenoid one. The codes that remain are the c1246 (master cylinder pressure sensor) and the increasing and decreasing pressure ones. Code c1246 also had a snowflake once I cleared the code. So I went into that and posted the results here as well. Lemme know if any of this info is useful for narrowing down the issue. Can you replace just the master cylinder pressure sensor? or is that just a fancy way of saying to replace the whole thing? Thanks again for helping! PS I also posted a image of the ABS data list incase that helps any!
     

    Attached Files:

  9. ChapmanF

    ChapmanF Senior Member

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    All of those Opn_Dets in the data list catch my eye. I wonder about the connections between the skid ECU (under the dash) and the brake actuator (out on the firewall).

    There will be some big multiwire connectors on both. I might be seen unplugging and reconnecting those some.
     
  10. priusmanneedhelp

    priusmanneedhelp Junior Member

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    ill try that when I get home. Thank you. Cross your fingers!
     
  11. priusmanneedhelp

    priusmanneedhelp Junior Member

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    I was reading a repair manual and it said to check my brake control power supply and that it should be 10-14v and mine was at 14.1 does that seem fine?
     
  12. Tombukt2

    Tombukt2 Senior Member

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    Are there I guess that part just sees battery voltage 12 volt that is so that seems like the car is ready and you checked and got 14 one which if you went back to your battery and checks it it would probably be the same good luck
     
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