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Brake control fault

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by jfh, Jul 20, 2005.

  1. jfh

    jfh New Member

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    I have a problem with my Prius T3 which so far seems to be beating the dealer and Toyota.

    It's behaves OK in the morning, but after about 20 minutes driving all four brake warning lights light up - VSC, ABS, yellow warning, red warning. Once lit they stay lit all day, driven or not (If parked they stay lit immediately on restarting.) They only clear when the car is parked overnight. The brakes work, but at reduced efficiency.

    Apparently the system believes there is low brake fluid, but that is spurious. So far the dealer has changed the brake fluid sensor, changed the braking ECU, and checked the intermediate wiring.

    The dealer has been unable to find anyone else that this has happened to.

    The possibilities as I see it are:

    1. A fault somewhere that is causing the ECU to misunderstand what is happening.

    2. A fault somewhere that is damaging the ECU.

    3. A condition or fault somewhere that is getting the software into an abnormal state.

    It looks to me that this is temperature triggered. It first happened when parked on an excepionally hot day. Each time it needs a long delay or a long cool to reset.

    Can it be a fault on anpther computer chip? On a computer power supply?

    Has anyone seen anything like this? Or have any thoughts? I would like my car back! The current state of play, I believe, is that the dealer has taken a computer trace and is waiting for Toyota to analyse it.
     
    #1 jfh, Jul 20, 2005
  2. popoff

    popoff New Member

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    No suggestions to offer but I hope the dealer has provided you with transportation, hopefully another Prius, while they are attempting to figure out what's wrong.
     
    #2 popoff, Jul 20, 2005
  3. hyBuild

    hyBuild New Member

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    I have experienced the same in my 05 just recently.

    It was on an extremely hot (desert) day. I was driving at about 65mph on a freeway. first it was the red brake warning light that came on. The road was clear, i kept driving. Then just as i exited on to a straight but long exit ramp, I started to apply the brakes lightly to bring the car to a slower speed -- The brake was very hard and I felt no reduction in speed. The car began what seemed like the bigining of a skid. I was forced to apply the brake even harder only causing the wheel to seem locked the car continued skidding toward the intersection ahead. withing this period all the brake warning lights light up - VSC, ABS, yellow warning, red warning. I was very locky the light at the intersection changed to green and the car had come to a lesser speed as a result of friction (mind you the road was very dry and HOT)

    Pretty shaken up, I drove jitterily slowly into a shopping center parking lot where I was meeting someone. The braking ahd returned to close to normal by the time I parked the car. The car was left parked for about 3 hrs. When I returned and started the car the brake warning lights were still on but after a few necessary tap on the brake while leaving the parking lot the warnings went away.

    I have not had a chance to have this looked at by the dealer because just shortly after leaving the parking lot, the car died upon leaving a traffic light. It had blown a fuse. this latter problem has to be looked at first before attempting to recreate the braking problem.

    I have read somewhere before that replacing the brake actuator sometimes malfunctions and replacing the actuator solves this problem. Please post what your technician finds, I'll do the same.
     
    #3 hyBuild, Jul 25, 2005
  4. jfh

    jfh New Member

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    To hyBuild:

    Thanks for your comments.

    The main functions of the red light are (I believe) to warn of low brake fluid level or worn brake pads. At the risk of stating the obvious those are the first things that needs to be checked. The dealer can interrogate the computer ti find out what it thinks is wrong.

    As for my car there is no progress yet - I'm just about to phone them again. But I will certainly post the resolution when it is found.
     
    #4 jfh, Jul 26, 2005
  5. DanMan32

    DanMan32 Senior Member

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    I would have preferred having the actual DTCs, but a bad accumulator seems to make a lot of sense. It certainly would indicate low pressure, which it may think is due to low fluid.
     
    #5 DanMan32, Jul 26, 2005
  6. jfh

    jfh New Member

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    I can now give an update on my initial report.

    The dealer has said they've found an intermittent connection in one of the ECU connectors and that a temporary repair appears satisfactory. They are currently replacing that part of the wiring harness.

    I haven't had the car back to test myself yet, but if you don't hear from me again on this you can assume that's the answer. I hope it is so!
     
    #6 jfh, Jul 27, 2005
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