Intermittent cooling light issue

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by camner, Sep 23, 2017.

  1. camner

    camner Junior Member

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    My daughter's Gen 2 Prius is having an oddity with the indicator lights related to the cooling system. She had her inverter water pump replaced recently (the "red triangle" warning light came on and this is what was diagnosed). Within a few hours of driving away from the garage the red triangle light came on again, and this time the main display screen indicated an issue with the cooling system. The diagnosis this time was a "slow leak" in the cooling system which would require eventually the replacement of the main water pump. The garage topped up the coolant level and off she went.

    A few days later, the red triangle light came on again, and once again the main screen indicated a cooling system issue. She checked the coolant level, and it was within a quarter inch of "full," so low coolant doesn't seem to be the issue. The red triangle light came on and stayed on each time she started the car for a couple of weeks, and then this morning when she started the car, the light was not on.

    Has anyone seen something like this?

    A second question: When the red triangle warning light comes on in a Gen 2 prius, is it supposed to stay on until it is reset by a garage, as is the case with many "check engine" lights, or can it reset itself?

    Finally, I know that the car has an issue with the Combination Meter (an intermittent failure of the dash lights). AFAIK, the red triangle warning light is not affected by the Combo meter issue, correct?

    Thanks in advance for the expertise here.
     
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    1. Did your daughter check the coolant level in the radiator itself (not just the overflow reservoir)? Often when the engine coolant pump bearing has a leak, that allows air in the system so that the system will not create a vacuum to bring in fluid from the overflow reservoir. Hence the reservoir will continue to show some fluid present, while the radiator level is dropping lower and lower.

    2. If the issue causing the red triangle disappears then the warning light will turn off.

    3. The red triangle warning light may not turn on if the combination meter ECU is intermittent.
     
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  3. camner

    camner Junior Member

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    No, she only checked the overflow reservoir.

    Thanks. This is good to know.

    I finally found a large detailed picture of the combination meter ECU, and the red triangle, check engine, and other "idiot" lights don't seem to be on that circuit board. Are you saying that if the combo ECU is intermittent then the appropriate idiot light may not come on? The dash only goes dark once a month or so. If the dash is on, can the idiot lights still not come on, or only when the combo ECU isn't lighting up?

    Thanks much for your response!
     
  4. Patrick Wong

    Patrick Wong DIY Enthusiast

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    The master warning red triangle is powered via circuits in the combination meter ECU, so I would not count on the warning light working if the combination meter ECU is inoperative. The check engine light might work if the ECU is dead, but again I would not count on that.

    The bottom line is that you should not count on receiving warnings via the dashboard warning lights or MFD messages. It is time to resolve all known problems so that she does not end up being stuck on the side of the road. Start by replacing the engine coolant pump and the combination meter ECU, then see what else comes up as an issue. Good luck.
     
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