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Loosing brakes, DTC C1246

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by andrewb, Jul 24, 2015.

  1. andrewb

    andrewb Junior Member

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    Hello,

    I have a 2010 GEN III Prius. I had a hard braking 2 days before I got VSC, ABS, STOP lights on the dashboard and C1246 code.

    I had reset the code and I got it again today. Both times the C1246 happened after a long strong press on the brake pedal (on the light), but I cannot repeat it in the controlled environment.

    I have a freeze frame data from the Techstream (image attached).

    I noticed that sometimes the car starts rolling even if I hold the break pedal. I have to press it further and it starts rolling again. It is not happening all the time, only when I play with the break pedal for sometime. Also the breaking fluid has never been changed.

    Unfortunately, I do not have access to the dealer, so I will need to deal it with myself. Can anyone point me to a right direction considering I have Techstream.
     

    Attached Files:

    #1 andrewb, Jul 24, 2015
  2. ChapmanF

    ChapmanF Senior Member

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    If you look up the C1246 in the diagnostics volume of your service manual on techinfo.toyota.com and follow to the indicated page, there will probably be several pages there of detailed troubleshooting steps you can use to spiral in on what your real underlying problem is. They're your brakes, so I would probably not be relying on secondhand information if it were me. At least, not as my primary source. For clarifying/filling in gaps in the manual, sure.

    -Chap
     
    #2 ChapmanF, Jul 24, 2015
  3. Patrick Wong

    Patrick Wong DIY Enthusiast

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    1. Odometer reading?
    2. It looks like the skid control ECU/brake actuator or the brake stroke sensor has failed. Consult techinfo.toyota.com for information regarding how to figure out which part has failed and how to replace them.
     
    #3 Patrick Wong, Jul 24, 2015
    Last edited: Jul 24, 2015
  4. andrewb

    andrewb Junior Member

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    Vehicle:
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    1. 52,000 miles
    2. Yes, I am looking. The 204 DTC subcode indicates:

    Either of the following is detected:
    1. The regulator pressure sensor output voltage does not
    correspond with stroke sensor and the readings remain
    out of specification for 0.5 to 5 seconds or more
    continuously.
    (The stroke sensor may be malfunctioning.)
    2. The regulator pressure sensor output voltage does not
    correspond with wheel cylinder pressure sensor and the
    outputs remain out of specification for 0.5 to 5 seconds
    or more continuously.
    (May be output with INF code 424.)

    Trouble Area
    - Brake pedal stroke sensor
    - Brake booster with master
    cylinder (Skid control ECU
    or brake actuator)
     
    #4 andrewb, Jul 24, 2015
  5. RRxing

    RRxing Senior Member

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    Did you have the Brake Booster Pump recall performed?
     

    Attached Files:

    #5 RRxing, Jul 24, 2015
  6. andrewb

    andrewb Junior Member

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    Thank you RRxing.
    No, my Prius does not seem to be eligible for this recall. The only recall I see is 14V053 - Update for Motor Generator ECU and Power Management ECU
     
    #6 andrewb, Jul 25, 2015
  7. andrewb

    andrewb Junior Member

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    I was able to reproduce and catch the error into TechStream event file.
    Two things noticed:
    a. The toyota prius manual indicates that SSC and SCC solenoids should have 0 A when brake pedal is released. However my car has 0.4 A and 0.6 A for these solenoids. This means they are opened. See solenoids.jpg attached.
    solenoids.JPG
    b. Pressure drops while I strongly hold the break pedal and the pedal slowly goes down until the DTC comes up. I cannot repeat it every time I press the pedal. Most of the time the pedal stays OK and solid.
    See sensors.jpg
    Sensors.jpg

    Can anyone advise on the SCC and SSC solenoids normal behavior. Should they ever be closed? They seem to close only after DTC. I am also attaching a techstream event file that contains the event log.
     

    Attached Files:

    #7 andrewb, Jul 29, 2015
  8. ChapmanF

    ChapmanF Senior Member

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    In your time on techinfo, have you by any chance discovered the New Car Features Manual yet? That's the one that includes the hydraulic diagrams of the brake system and all the sensors and solenoids and goes into the whole theory of operation ... the background that the other manuals just sort of assume you have. I'm leery of trying to extrapolate anything for you from my Gen 1 book because the changes are too extensive ... even the names of the solenoids have changed. But by looking in the book for your own model, you should find a lot of helpful stuff.

    -Chap
     
    #8 ChapmanF, Jul 29, 2015
  9. Patrick Wong

    Patrick Wong DIY Enthusiast

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    I think that SSC and SCC are supposed to close when the brake actuator pressure is below normal (i.e., this is a fail-safe mode.)

    As Chap indicated, the NCF provides lots of detail about how the various solenoids open and close based upon different braking modes, whether hill start assist is working, when the system fails, etc.

    I think it is highly likely that the brake actuator needs to be replaced. My suggestion is that you perform the repair manual troubleshooting to eliminate the brake pedal stroke sensor as a possibility, then you can be comfortable that the actuator is at fault.
     
    #9 Patrick Wong, Jul 29, 2015
  10. andrewb

    andrewb Junior Member

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    Thanks for pointing me to NCF. Here is the brake system diagram with correct names:
    brake-diagram-prius.png
    I have tested the system according to the repair manual troubleshooting guide (except the actual Hydraulic Pressure measurements on the wheels) and everything seems to be fine. Intermittent problems check wasn't done.

    I have also reviewed the solenoids logic from Techstream and it seems to be corresponding the NCF (including SSC and SCC). Unfortunately, NCF does not explain the logic in dynamics. For example, should the pressure drop on one of the sensors while I hold the brake pedal?

    I am not able to reproduce the error again (without driving). I will try again while driving. Probably I should start from simple, do air bleeding.

    It would be very helpful if Techstream owners can record a similar even log file for comparison purposes.
     
    #10 andrewb, Jul 30, 2015
  11. andrewb

    andrewb Junior Member

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    New observations, when I press and hold the brake pedal once - it works fine. However when I release it a bit and press again - it starts floating down very very slow. It looks more like a problem in master cylinder of an old car - rubber seals or spool valve problem.
     
    #11 andrewb, Jul 31, 2015
  12. RL Prius

    RL Prius Junior Member

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    Hi Andrew, may I ask you how did you get the error code C1246. Was the check engine lit up?
    reason I am asking is my 2010 Prius II has similar behavior a while ago. I was never able to duplicate or even how to describe it.
    One day I felt I am loosing braking power. but one day work normal.....
    When I felt it was acting up, not only it requires to push the pedal really hard in order to stop the car. . Also if I stop at red light, my brake won't hold the car. I have push the pedal real hard. It is like an old car with a very high idle rpm set.
     
    #12 RL Prius, Aug 1, 2015
    Last edited: Aug 3, 2015
  13. andrewb

    andrewb Junior Member

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    RL Prius, I found it hard to reproduce. However there were three things that are always present before the error:
    1. Not important: Happens after some driving, never had it right after the car is turned on.
    2. Happens at long traffic light, but only when you keep the pedal pressed very hard. But not too hard so no hill assist comes up.
    3. Most important: you press the pedal hard, release it a little and then press again. You can feel the pedal going down very slow. When it reaches the floor, the error comes up.

    BTW, I did the air bleed including stroke emulator bleed - there is no change with the pedal behavior as described in item 3.
     
    #13 andrewb, Aug 3, 2015
    Lawrance likes this.
  14. andreimontreal

    andreimontreal Active Member

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    Look here on page 5 - at post 88 - I think I've managed to understand how the system works and what matters. That should be Gen 3 Braking System. I know this is an old thread but it helped me with the diagram/full NCF so I hope it will help future generations.

    SSC and SCC should always have current passing through and just like andrewb (another andrew here) I have 0.42Amps/0.6 Amps. THe SCC can vary as braking occurs. Anyway see the explanation.
     
    #14 andreimontreal, Aug 10, 2020
  15. Brittany Maclaughlin

    Brittany Maclaughlin Junior Member

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    Hi! I have my brake, abs, and traction warning lights appearing on my Toyota Prius 2011 - I took to Dealership to evaluate (the OBD2 returned no codes, so they needed the TechStream (?) diagnostic and they said my brake booster needed replacement - $1700 repair. I did a search on this site, and another thread indicated a brake assembly recall for Prius 2011, but the dealership indicated the code that was returned (C1246- sub code 204) didn't cover the recall.

    I have not yet proceeded with the fix (was going to shop around!). Can anyone offer any advice based on this code (C1246- sub code 204) Note:, i dont notice anything wrong with the brakes except the warning lights. I'll probably just get another estimate but any feedback appreciated (noticed the reporter of this problem had same issue!!).
     
    #15 Brittany Maclaughlin, Oct 18, 2021
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