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Yellow Brake Warning Light

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by salguod, Nov 9, 2016.

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  1. salguod

    salguod Member

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    My wife's Prius has had an intermittant yellow circle with parentheses and exclamation point for several weeks now. Initially it was accompanied by a TPMS warning light, but is not now. There are no other warning lights aside from the Maint. Req'd because it's due for an oil change. [EDIT: I should add occasionally the cruise will not engage and the cruise light flashes.]

    When it first appeared I checked the air in all tires and found one low. One thread here indicated that a low tire can sometimes throw both lights. More air corrected the TPMS light and seemed to fix the other, but it returned fairly quickly.

    I've checked the brake fluid and the brake pads. Fluid level is fine, pads have plenty of life left. I have not pulled a rear drum to check the shoes.

    I plugged in my OBDII reader but it was not able to give me any info.

    Plenty of posts here tell me that this light indicates a brake system problem, but few specifics. One post indicated the 12V battery cables had not been plugged in properly when changed, but I've not touched the 12V. The brakes show no symptoms of any problem, only the light.

    Can anyone shed any light on what specific brake issues may cause this light to come on? I generally fix my own vehicles and prefer not to spend the time and money at the dealer if I can avoid it.
     
    #1 salguod, Nov 9, 2016
    Last edited: Nov 9, 2016
  2. JC91006

    JC91006 Senior Member

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    What year is the prius? Can you take a picture of the warning light?
     
    #2 JC91006, Nov 9, 2016
  3. salguod

    salguod Member

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    In my signature - 2007 Touring.:D

    I should also mention that occasionally the cruise will not engage and the cruise light flashes. I'll add that to the original post.
     
    #3 salguod, Nov 9, 2016
  4. salguod

    salguod Member

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    Light looks like this, without the word BRAKE:

    [​IMG]
     
    #4 salguod, Nov 9, 2016
  5. JC91006

    JC91006 Senior Member

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    You can see if the brake lamp switch is causing problems. It's located at the brake pedal. That would be my guess
     
    #5 JC91006, Nov 9, 2016
  6. salguod

    salguod Member

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    What would you suggest to look for?
     
    #6 salguod, Nov 9, 2016
  7. JC91006

    JC91006 Senior Member

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    Have your wife get behind the car and you press the brake. See if it lights
     
    #7 JC91006, Nov 9, 2016
  8. salguod

    salguod Member

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    Went to the garage in the dark and pushed the brake. All 3 lights lit up.

    I see this post that indicates a new hybrid or engine ECU may be needed (ouch!)

    This post shows how to check for "blink codes", I may look into that tomorrow night.
     
    #8 salguod, Nov 9, 2016
  9. JC91006

    JC91006 Senior Member

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    Or you can get the codes read. Do you feel like your brakes feel normal? Or lacking power brakes and battery regen?
     
    #9 JC91006, Nov 9, 2016
  10. salguod

    salguod Member

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    Brakes feel fine, no different. No drivability issues at all, except for the cruise not working occasionally. The cruise light does not always blink whenever the brake light is on and the brake light isn't on all the time.
     
    #10 salguod, Nov 9, 2016
  11. JC91006

    JC91006 Senior Member

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    Well I really think that would be a brake lamp switch problem.

    Does the ac air recirculation button work on your steering wheel?
     
    #11 JC91006, Nov 9, 2016
    Last edited: Nov 10, 2016
  12. mmmodem

    mmmodem Senior Taste Tester

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    A brake light could mean you're low on brake fluid.
     
    #12 mmmodem, Nov 10, 2016
  13. salguod

    salguod Member

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    The evidence doesn't point to a brake lamp switch to me at all. That switch has two function that I'm aware of, allow you to shift from park and turn on the brake lights. The brake lights work fine, the car shifts fine so there is no evidence that the switch isn't functioning right There are also no posts here that I've found relating this light to the brake light switch.

    I'm not sure why you are asking about recirc, but I believe it works fine, although we rarely use it. We leave it in "auto" most of the time. The two refrost buttons on the wheel are not functional, but the defrost does work if selected from the touch screen.

    As I mentioned in my first post, the fluid level is fine.
     
    #13 salguod, Nov 10, 2016
  14. andrewclaus

    andrewclaus Active Member

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    Good advice above, even the apparent red herring about the air recirc button--that would indicate a problem with the spiral cable in the steering column, affecting the cruise but unrelated to the brakes.

    If you're going to be working on this car, you should invest in the correct scan tool. Many of us use a MiniVCI cable with Techstream software. It's only $20 or so and you need an old WinXP or 7 laptop. The Prius ABS system is fairly complicated and has a lot of proprietary codes that cannot be read with generic scanners. I've never heard of a flashing cruise light, but that may indicate a fault with that system. There are even fault codes for the cruise control system.

    The brake switch or associated wiring is common to both systems and that's a logical place to look carefully. If it is the ECU, they are available salvaged on eBay for as low as $30.
     
    #14 andrewclaus, Nov 10, 2016
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  15. salguod

    salguod Member

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    Got a link for the MiniVCI cable & Techstream? My laptop is Win 10 64bit, however, and it seems that may be problematic.
     
    #15 salguod, Nov 10, 2016
  16. digbywombles

    digbywombles Junior Member

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    It is possible to install on a 64-bit system, but a little fiddly. I managed with instructions on the net (I have Windows 7, 64-bit). The software installs fine, it's the drivers that need to be manually installed.
     
    #16 digbywombles, Nov 10, 2016
  17. JC91006

    JC91006 Senior Member

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    The brake lamp switch also has a function that disables the cruise control. When it's on, you press the brake and the cruise control will disengage. If that switch is malfunctioning, it'll explain the problem you have with cruise control.

    The air recirc question has to do with the function of the spiral cable, which is also connected to your cruise control toggle. Since that cable can fail with age, it usually disables the air recirc first and then other systems fail along the way as it ages.

    Without techstream, this is a process of elimination
     
    #17 JC91006, Nov 10, 2016
  18. salguod

    salguod Member

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    I'm looking into Techstream, but it does seem that a new spiral cable is in order since I have some inoperative steering wheel controls.

    Does the Techstream software typically come with the cable?
     
    #18 salguod, Nov 10, 2016
  19. dolj

    dolj Senior Member

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    Yes. If you ensure the cable driver is 64-bit, it will make your install of the cable driver much easier. Installing the 32-bit driver on a 64-bit system is a little bit of smoke and mirrors combined with a bit of hoop jumping dance.

    In any case, you may want to consider creating a Win XP or Win 7 virtual machine and installing Mini VCI and TS in there.
     
    #19 dolj, Nov 10, 2016
  20. salguod

    salguod Member

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    I've ordered a 64 bit Mini VCI from eBay. I'll report back when I know more.
     
    #20 salguod, Nov 11, 2016
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