Brake warning light and engine light come on intermittently

Discussion in 'Generation 1 Prius Discussion' started by Bruce Berquist, Oct 9, 2021.

  1. Bruce Berquist

    Bruce Berquist New Member

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    2003 Prius sedan.

    Brake light and Engine light come on intermittently after a good period of time driving. Seems to happen when slowing down from a long period of time at highway speed, and also when turning at an intersection after the same conditions.
    As a note of interest, the ABS light did come on but only in one occasion.

    No trouble codes comes up in the OBDII except for, at the moment, the Red Triangle always comes on due to a p3006 code which I have ordered replacement cell modules to repair it.

    When this brake and engine light comes on the the brakes still work fine but engine runs at a high rpm.
    When I pull over and shut off the engine I then notice squishy brake pedal, but then when I restart the engine everything resets to good with no brake or engine light, and the brakes function with no problem.

    I have been perusing all posts regarding brake light issues but have not seen any responses that are directly helpful to this issue I am having.

    I am curious as to whether this issue is related to p3006 out of balance SOC in my HV battery?

    My car runs, drives and brakes just fine.
    I don't believe that the brake light issue is related to an actual "mechanical" problem since the brake light issue is not consistent enough for a mechanical problem, and when it happens it completely resets when the car is restarted.

    I'm hoping some people will have some good insight on this occasional but nagging issue.
     
  2. nimblemotors

    nimblemotors Re Member

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    hmmmm, I wonder if its because of the battery, the car can't brake using regen because the battery can't absorb any current,
    and basically after a long drive the battery is full. Just a wild guess. I'm not even sure what you mean by brake and engine light?
     
  3. Bruce Berquist

    Bruce Berquist New Member

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    You are thinking in the same direction I am. I am just trying to determine that it is a correct direction, and also see if I should be looking in any other direction on this.

    I mean brake warning light on the dash, same light as for the parking brake. And I mean engine light as in the engine maintenance light on the dash.
     
    #3 Bruce Berquist, Oct 10, 2021
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  4. Bruce Berquist

    Bruce Berquist New Member

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    Usually a trouble code will come up to whatever is triggering the engine light.
    I have OBDII software that reads all of the Prius ECUs but no codes are coming up, except for the p3006 HV battery code which is related to the red triangle dash light.
     
  5. ChapmanF

    ChapmanF Senior Member

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    If the brake, ABS, or VSC lights come on, you can try getting the blink codes from the brake system. Eliminates questions of why the scan tool reports no codes.
     
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  6. Bruce Berquist

    Bruce Berquist New Member

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    Thank you but I only got the ABS light once and that was just after I replaced the brake pads and shows.
    Since then I have no ABS light.
    Only the occasional brake warning light with the check engine light, along with the red triangle.
    The only code is P3006.
     
  7. ChapmanF

    ChapmanF Senior Member

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    Sorry, had the Gen 1 long enough ago I had forgotten some of the differences.

    So your brake ECU controls two warning lights, the red one spelled BRAKE and the yellow one spelled ABS.

    [​IMG]

    The brake ECU controls the ABS light directly: there's a wire that's an output from the brake ECU, and goes to the combination meter, and lights the light.

    The brake ECU controls the BRAKE light less directly: there's a wire that's an output from the brake ECU, but it goes to the body ECU, and the body ECU sends a BEAN message (no CAN yet!), and the combination meter gets the message, and lights the light.

    The brake ECU has direct wired inputs from the parking brake pedal switch and the brake fluid level sensor.

    It asserts its BRAKE light output if the park pedal switch is on, or if the fluid level is sensed low, or if DTC C1213 or C1259 is present.

    No matter which light is on as a warning, when you jumper to get blink codes, the ABS light (in Gen 1) is the one that will deliver the codes.

    The workup for the BRAKE warning light of course steps through all of those bits: the park pedal switch, the fluid level sensor, DTCs, the combination meter, the BEAN, and the brake ECU.
     
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  8. ammdb

    ammdb Junior Member

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    What your describing is limp mode, when the car gives up on the main battery and gets all its torque from the internal combustion engine. The engine revs to generate the electricity that would otherwise come from the battery. When this happens there's no regenerative braking, which is why the break light came on.

    After battery pack is repaired or replace, and the P3006 code is taken care of, the break light should stay off.
     
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  9. ChapmanF

    ChapmanF Senior Member

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    If that's the case, C1259 will be retrievable as a brake system code (or 5 9 blinked on the ABS light).
     
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  10. Bruce Berquist

    Bruce Berquist New Member

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    Thank you. You are confirming my suspicions on this. I ordered a package of Cells so that I can restore and balance my Main Battery next week.

    I am thinking that this will not only solve the Brake Warning Light issue, but also a few other minor bothersome quirks, such as the cruise control shutting down while I'm using it.
     
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