ECM fried by coolant control valve repair?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Jacob Gerlach, Sep 25, 2018.

  1. Jacob Gerlach

    Jacob Gerlach New Member

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    I took my 2009 Prius in for a check engine light caused by a stuck coolant control valve. Immediately after picking up the car from this repair (5-10 minutes), I got the master warning on the dashboard, followed by a high coolant temperature warning on the top line of the display screen.

    The dealership initially diagnosed the temperature warning as a electrical fault caused by low battery voltage and replaced the battery. I then got the exact same indications within 20 minutes of driving time after the battery was replaced.

    After further troubleshooting, they determined that the ECM was failed. This diagnosis was based on a flow chart that dead-ended with replacing the ECM since no other voltages/checks were UNSAT.

    The idea that a high coolant temperature warning suddenly occurred by coincidence after working on the coolant control valve seems like an impossible coincidence to me, but the dealership swears that there is no way they could have damaged the ECM with the work they did and want me to pay $1200 to repair it.

    They agreed that if any other Prius mechanic can explain with a schematic how it was possible, they would take responsibility and not charge me for the repair.

    Any ideas?
     
  2. JC91006

    JC91006 Senior Member

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    When the replaced the coolant valve, most likely they didn't replace all the coolant that was removed. If the mechanic is not familiar with the Prius, there's a chance they didn't get the air out and fill the car with coolant. Your car overheated from the lack of (low) coolant. Nothing else.
     
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  3. Jacob Gerlach

    Jacob Gerlach New Member

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    They did bleed the system after replacing the valve.
    It was a Toyota dealership, so they are definitely familiar, and mentioned having done this particular repair a few times.

    I am still waiting on an email back confirming that they test drove the car and didn't get temp alarms, but they are saying that replacing the ECM cleared up the problem.
     
  4. DLC82SV

    DLC82SV Member

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    You took the words right out of my mouth JC91006. Purging all of the air can be very tricky and time consuming and is imperative that it be done completely and correctly! They should be held accountable in my opinion as well OP!

    Posted via the PriusChat mobile app.
     
  5. Elektroingenieur

    Elektroingenieur Senior Member

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    There are three wires connected directly between the water valve (coolant flow control valve) and the WSL1, WSL2, and WBAD terminals of the ECM. These are shown in Electrical Wiring Diagram (available by subscription to techinfo.toyota.com, and to the dealer on Toyota TIS) in the Engine Control part of the System Circuit section:

    WaterValve2009.png

    While troubleshooting and replacing the water valve, if a technician caused any of these lines or circuits to be exposed to voltages or currents in excess of those for which it was designed, or if there was an electrostatic discharge, the ECM could have been damaged. Without the ECM design and test specifications, which Toyota doesn’t publish, it’s hard to assess the likelihood of this, but it is possible.

    It’s usual in the design of electronic control units for automotive applications to include protection from such abuse, but that may not have been done here, or the protection may have been insufficient. In the Repair Manual, Toyota indirectly acknowledges this possibility, with the warning, “Before performing electronic work, disconnect the cable from the negative (-) battery terminal to prevent component and wire damage caused by accidental short circuits.” (This is in the Precaution section of the Introduction, by the way.)

    If the dealer won’t absorb the whole cost, perhaps you could offer to pay for the new ECM, discounted to their cost (not the usual retail price), if they agree to pay for the labor.
     
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  6. exstudent

    exstudent Senior Member

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    OP just has to ask the service manager if the ding dong tech followed the Toyota Service Manual procedures?
    Have the manager/tech tell you what the procedures are.
    If he/she doesn't state disconnect NEGATIVE battery cable, Toyota repair procedures were NOT followed.
    This can be corroborated by the original return of the vehicle with the correct time and radio presets maintained, assumed.

    The 12V memory savers that plug into the cigarette socket, will not work for the Prius b/c of how the cigarette socket is wired. Furthermore, this article says industry experts (collision repair people) do NOT recommend use of such devices.
    Memory savers not recommended by industry experts | Search Autoparts

    Good Luck. Hope they cave in.
     
  7. Dxta

    Dxta Senior Member

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    I think what happened to that ECU might be a coincidence. I don't just see how what they replaced, could ha e caused the problem. The coolant valve has connectors I think on it. Replacing the valve does not have to involved wire splicing, or so. So, there should be no way a short could have occurred that fried the ECU.
    My thought is that there may have being another thing that caused it.
     
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  8. Dxta

    Dxta Senior Member

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    To the OP. If you want to get to the root of the problem, and of you are a DIYer, you could try taking a look through the coolant valve harness wires, and see of there had been any signs of splicing the wires, or coolants contacts(I doubt that would cause the ECU to burn out).
     
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