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Check engine light keeps going on and off, what to do?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Connorp, Jul 10, 2023.

  1. Connorp

    Connorp New Member

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    2007 Prius
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    ----USA----
    In the past couple weeks the check engine light on my 07 Prius has gone on 3 times. The first time it went off I adjusted the gas cap and it went off the next day. It went on again this Thursday, but then turned off today when I drove to the store. Later on in the afternoon though, it turned back on when I made another errand trip. I adjusted the gas cap a couple days ago, but in between the two errands I did today I adjusted nothing.

    The car drives totally fine and I'm able to start it without issue. Two things I've noticed though. First, the two times I've gotten gas this weekend, I've only been able to fill about 4-5 gals before the pump stops and won't let me fill any more. This is after the "add fuel" message comes up with one blinking bar on the gas gauge. When I fill it, the fuel gauge still goes full, even though I used to be able to put 6-7 gallons into an empty tank.

    Second. Earlier in the day on Thursday, before the light went on, my key fob stopped working. I'm still able to lock the car with the button on the door but the fob still doesn't work even though I changed the battery.

    Any ideas?
     
  2. PriusCamper

    PriusCamper Senior Member

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    Sounds like 3 separate and unrelated issues. The dash light logs an error code that tells you what the problem is. Any auto parts store will read the error code for you. Also buy one of these to keep in your glove box: Hybrid battery diagnostic and repair tool for Toyota and Lexus so you can use phone apps, like Dr. Prius app and others to read and clear error codes. It might eventually be the difference between being able to continue to drive vs. waiting for a tow truck.
     
  3. bisco

    bisco cookie crumbler

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    start with a free 12v load test at auto zone. check the connections too, especially neg to ground.

    how is the oil level?
     
  4. Brian1954

    Brian1954 Active Member

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    If the check engine light turns on, you have trouble codes that need to be retrieved. The trouble codes will help to determine the problem with the car.

    Posted via the PriusChat mobile app.
     
  5. Connorp

    Connorp New Member

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    I'll try that text at auto zone. Oil level is good, I had it changed recently.
     
    bisco likes this.
  6. Connorp

    Connorp New Member

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    Went to autozone and the error code was "coolant flow control valve position sensor stuck" and suggested a new heater control valve. I opened up the hood and saw the engine coolant was fine, but the inverter coolant was low. Can I top it off with Toyota Super Long Life Coolant and be good or do I have to bleed and replace? Prius is at about 115k miles.
     
  7. Brian1954

    Brian1954 Active Member

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    This is a common problem on a Gen 2 Prius. This does not need to be fixed right away. Do you plan on replacing the valve yourself or taking it to a mechanic?

    Posted via the PriusChat mobile app.
     
  8. bisco

    bisco cookie crumbler

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    you can just top it up
     
  9. ChapmanF

    ChapmanF Senior Member

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    which won't fix the control valve, but will stop the coolant being low
     
  10. Connorp

    Connorp New Member

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    ----USA----
    The check engine light went off again after I had the error code read at Autozone, though I still went and filled the coolant. I'm going to wait and see if the light comes on again. If it does, and the coolant level is fine, I will probably take it in. I found a post on Priuschat about how to replace the heater control valve but I have little to no experience working with the car so I will likely take it to a mechanic unless you guys think it's an easy enough fix. That post also said that sometimes when that check engine code (P1121) goes on, it simply means the coolant level is low. So I'm not sure if I solved the root of the problem or not.
     
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