Completed coolant drain and fill on 2007 Prius; MIL light need reset, or goes off on its own?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by fishingtimoteo, Jun 23, 2016.

  1. fishingtimoteo

    fishingtimoteo New Member

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    Just finished a drain and fill on my 2007 Prius; I've done several cycles of bleeding the air out of the system involving: engaging the coolant heat storage tank pump, squeezing the hoses, opening bleeder valve, running the engine for extended periods of time, but the check engine light is still on. My question is will it go off on its own, or do I have to clear/reset a diagnostic trouble code. I read that disconnecting the connector to the coolant heat storage tank (which I did per the repair manual instructions) may cause a check engine light to appear. I also read that having significant air still in the coolant system will also cause the check engine light to appear. Is there any way to know the reason it is appearing without using an OBC II scan tool (I currently don't own one)? Thanks in advance.
     
  2. johnnyb588

    johnnyb588 Member

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    My (limited) experience with my Prius is that it stores codes longer than I'm willing to wait to reset. I have driven multiple miles and run the car for 30+ minutes while its stored codes never dropped. Upon doing a reset (disconnecting battery is my method), the codes clear and don't come back.

    A scanner (especially mini vci) will give you the reason for the code.

    My course of action, if I were you, would be to reset the ECU and see the if the light comes back. If everything was done correctly and it's just showing you a stored code, then the light won't come back on. If it comes back on, it's time to get a scanner on it to figure out what's going on.
     
  3. JC91006

    JC91006 Senior Member

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    The check engine light is an emissions error, changing coolant usually doesn't fix that.

    If you have a problem with the 3way valve, then you would need to change that before the coolant change
     
  4. fishingtimoteo

    fishingtimoteo New Member

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    The check engine light was not on before the coolant change. To reset the ECU, I went ahead and disconnected the battery for about 30 seconds and then reconnected it; upon starting the car, the check engine light went off. I have not driven it yet, but when I run some errands later today, I will monitor the display to be sure it does not come on again. I can't be positive until I take a drive, but I feel confident that the coolant change/bleeding process has been sufficiently completed. I'll post tomorrow with a final(hopefully) update.
    Thanks guys!
     
  5. fishingtimoteo

    fishingtimoteo New Member

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    I know it's been a while, but needless to say, the check engine light has not come back on and everything is great! Thanks!
     
    trungdok likes this.
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