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lost braking and steering while driving

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by whodat, Sep 9, 2010.

  1. whodat

    whodat Member

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    While driving a mountain road (hwy 17) going downhill this morning I lost power braking and power steering and a got the following error message on the display

    TRANSMISSION P LOCK MECHANISM

    PARK CAR ON FLAT SURFACE AND APPLY BRAKES

    I was able to stop the car on a flat area. I turned the ignition off and then restarted the car and the power steering and brakes came back, but the red triangle remained. I drove to the Toyota dealership and left the car for service.

    Has this happened to anyone? Any ideas about the root cause of this problem?
     
    #1 whodat, Sep 9, 2010
  2. firepa63

    firepa63 Former Prius Owner

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    What was/is the condition of the 12v battery? Is it the original battery?
     
    #2 firepa63, Sep 9, 2010
  3. Patrick Wong

    Patrick Wong DIY Enthusiast

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    I know Hwy 17 well, that is not a great place to lose steering and braking assist on the curvy portions of that two-lane (in each direction) highway with the following traffic close on your rear.

    Sounds like the 12V bus voltage dropped down suddenly. My guess is that the DC/DC converter in the inverter had a problem (usually due to a failed inverter coolant pump) and that the 12V battery lacked the power to keep the electrical systems running.

    What other warning lights came on besides the master warning triangle? I would be very interested to know what DTC had been logged.
    It does sound like the 12V battery needs to be replaced.
     
    #3 Patrick Wong, Sep 9, 2010
    2 people like this.
  4. whodat

    whodat Member

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    Battery symbol also came on and car symbol with !.

    Its the original 12V battery.

    If the issue is the 12V battery, then why was I able to start it again, and why did it trigger while I was driving down hill regeneratively braking?

    Perhaps if the inverter coolant pump fails, the DC/DC converter gets hotter and there is larger voltage drop - then turning off the car, the DC/DC cools, there is less voltage drop and then the car can function properly again?

    The car is at the dealer who still awaiting a hybrid mechanic to look at the car.
    Stay tuned.
     
    #4 whodat, Sep 9, 2010
  5. Patrick Wong

    Patrick Wong DIY Enthusiast

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    The car symbol with ! which appears in the upper left corner of the MFD is the hybrid vehicle warning icon.

    Where did you see the battery symbol? Did that appear in the MFD or on the instrument panel?

    My guess is that the root cause of the problem is a failed inverter coolant pump. Once the DC/DC converter overheated and shut down, the 12V battery lacked sufficient power to keep the car running, so the steering and braking assist systems shut down. Hence the 12V battery exacerbated the situation but was not the root cause.

    When you tried to restart the car, the 12V battery had sufficient power to boot up the ECUs. Apparently the DC/DC converter had cooled down sufficiently by then to resume operation.
     
    #5 Patrick Wong, Sep 10, 2010
  6. Codyroo

    Codyroo Senior Member

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    1) I am very glad to hear you are OK. I too have driven on Hwy 17 and I understand how steep and winding it is (and how fast people drive under those conditions

    2) I hope you car is fixable without being overly expensive

    3) I'm still glad to hear you are OK. This could have been very bad.
     
    #6 Codyroo, Sep 10, 2010
  7. mgm_az

    mgm_az New Member

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    These are also the same symptoms I had when my inverter coolant pump failed. I was absolutely convinced it was the 12V battery at the time.

    Good luck finding a pump - it is hit or miss.

    My suggestion to you: if the dealer says they don't have the pump and it is backordered (told me for a month!), do the the legwork yourself and find one. Look at other dealers or on Ebay. Just make sure it is the genuine article and a new part or the dealer will not install it.
     
    #7 mgm_az, Sep 10, 2010
  8. whodat

    whodat Member

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    I got the car back from the dealer. They could not find anything wrong. Print out from dealer:
    131297 found code P0A08. dc/dc converter status circuit. checked aux battery-passed load test. Check cable connection from auxiliary battery terminal - cables connections are secure. Checked inverter water pump coolant level and operation-pump is working.
    So they replaced the aux battery, and so far the car is working fine.

    When your inverter coolant pump failed did it fail intermittently, or hard failure?
    Thanks
    Dave
     
    #8 whodat, Sep 12, 2010
  9. whodat

    whodat Member

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    Update on this problem. This was solved by replacing the 12V AUX battery. 7 weeks of everyday driving with the new 12V AUX and not a repeat of the problem below!


     
    #9 whodat, Oct 27, 2010
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  10. Silver bullit

    Silver bullit Right Lane Cruiser

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    You say the 12 volt battery passed the load test. I don't understand why replacing the aux battery would solve the problem. Anyway glad your car is running well.
     
    #10 Silver bullit, Oct 27, 2010
  11. Hal W

    Hal W New Member

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    How easy was it to steer and brake when you lost assist? H
     
    #11 Hal W, Oct 27, 2010
  12. bisco

    bisco cookie crumbler

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    have you driven down hwy 17 again?
     
    #12 bisco, Oct 27, 2010
  13. whodat

    whodat Member

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    The steering and braking loss was gradual, not abrupt. Since I was going down hill I waited until a flat spot to attempt to brake.

    Getting the car to stop from 50 mph to zero required alot of force.
     
    #13 whodat, Nov 1, 2010
    1 person likes this.
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