Power button unresponsive in hot weather

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by DrowningInteger, Jun 23, 2025.

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  1. DrowningInteger

    DrowningInteger New Member

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    Yeah I've been putting the key in the slot just to make sure it wasn't a problem with the key.
     
    #21 DrowningInteger, Jun 26, 2025
  2. DrowningInteger

    DrowningInteger New Member

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    I pulled the glove box out to check out some of the wiring in the dash and I saw this broken brown wire. What is this for? The photo was taken in the glove box area looking at the driver side. It's near the key fob slot.

    I also found a little mouse house and some droppings in the tray under the blower motor so I'm preparing myself for some rat damage.
     

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    #22 DrowningInteger, Jun 27, 2025
    Last edited: Jun 27, 2025
  3. WuTang69

    WuTang69 New Member

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    Woah, that's super weird for a Prius, especially when it's hot! Since disconnecting the 12v battery helps, it sounds like something might be getting stuck or overheated, maybe in the "combination meter" (that's the dash display). A lot of people with older Priuses have problems with that thing. You could try looking up "Prius combination meter repair" on YouTube, it's a common fix!
     
    #23 WuTang69, Jun 30, 2025
  4. DrowningInteger

    DrowningInteger New Member

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    Ok I think I figured this out. I replaced the negative battery cable with a new OEM cable from Toyota and it hasn't had any issues starting even after sitting a few days in 90 degree weather. I guess it really does always comes back to the 12v system. It turns out the broken wire in the dash was unrelated to the starting issue, but it did fix the intermittent screen flickering issue I was having.
     
    #24 DrowningInteger, Jul 14, 2025
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  5. DrowningInteger

    DrowningInteger New Member

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    It seems I may have spoke too soon. The car wouldn't turn on again today, but I've noticed if the key is far away from the car when it's off, no issues. But as soon as the key is within like 20 feet of the car for too long, like 15-20 minutes, it won't turn on until I disconnect and reconnect the 12v battery. But before that, I was able to drive it long enough to get a P1121 code. The heater doesn't seem to work so I'm guessing that's probably why. Is there any way a failed coolant control valve can be related to the car not turning on? The car does go into Ready mode without issue when it does turn on.
     
    #25 DrowningInteger, Jul 18, 2025 at 5:22 PM
    Last edited: Jul 18, 2025 at 5:36 PM
  6. ChapmanF

    ChapmanF Senior Member

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    Do you have a larger or zoomed-in version, or one where you could add a circle or arrow for the wire you mean? I saw some brown wiring in your attachment, but I'm not sure I saw a break.
     
    #26 ChapmanF, Jul 18, 2025 at 9:47 PM
  7. DrowningInteger

    DrowningInteger New Member

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    Yeah I got a different angle when I pulled the dash apart. There's two brown wires that were broken that I reattached to the metal piece they broke off of.
     

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    #27 DrowningInteger, Jul 18, 2025 at 10:21 PM
  8. DrowningInteger

    DrowningInteger New Member

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    I got a little more information about this that might be helpful. I was told the car was taken to a Toyota dealership and they didn't know what was wrong with it, but I was able to get the actual notes on the car and it turns out that wasn't entirely true. Are key fobs stored in this transponder ECU in the dash or is that stored somewhere else? Like if it's replaced with a new or used one, will the key have to be re-programmed to the new unit?

    "
    ENGINE CONCERN ~|~CUSTOMER REPORT WON'T START UNLESS YOU DISCONNECT AND RECONNECT POSITIVE TERMINAL. CUSTOMER HAS DISCONNECTED THE TERMINAL FOR NOW. ~|~CONFIRMED CONDITION. REMOVED DASH. FOUND WHEN TRANSPONDER KEY ECU IS UNPLUGGED AND PLUGGED BACK IN VEHICLE IS ABLE TO START. REC REPLACE ECU AND RECHECK. DURING REMOVAL RODENT NEST WAS FOUND INSIDE BLOWER MOTOR AND CABIN FILTER. REPLACE CABIN FILTER. ~|~NO REPAIRS DONE AT THIS TIME
    "
     
    #28 DrowningInteger, Jul 23, 2025 at 12:13 PM
  9. hurricos

    hurricos Junior Member

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    It does. There's a relationship between the state in the circuitry in the combination meter and that in the on button.

    I don't recall exactly whether the combination meter actually controls the button, or if there's another ECU that handles the interplay.

    A symptom of a dying combo meters is that the button and meter occasionally become "out-of-sync" with the rest of the car. Getting the combination meter working again usually fixes this.

    I'd also add, heat will change the ESR of electrolytic caps -- this particular comparable is usually the one which drifts combination meters into failure.

    TL;DR replace the capacitor folks usually replace in the combination meter. If you can't find which one this is, I'll help you. It's a few hours of work, but it's very good to isolate this -- three of the four Gen2 Prii I've worked on have had their combination meters fail exactly this way (the fourth has yet to fail), and have had synchronization issues as a result.

    I follow this video --
    -- please forgive how quickly this Youtuber runs through the process.

    For removing the capacitor: if the original black-plastic-collared SMD part is still there, I HIGHLY recommend this method of removal, which avoids the risk of pulling up traces by ensuring the strain is directed at the interface between the plastic and capacitor-side of the SMD capacitor ribbon leads, instead of the board side of the leads: https://youtube.com/shorts/aEusLVWOEwg
     
    #29 hurricos, Jul 23, 2025 at 5:10 PM
    Last edited: Jul 23, 2025 at 5:20 PM
  10. hurricos

    hurricos Junior Member

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    How far to the right-side of the dash is this (you're not in a left-hand drive country, right?)

    None of the meaningful circuitry exists on the right side. I ask because you mentioned glovebox.
     
    #30 hurricos, Jul 23, 2025 at 5:21 PM
  11. DrowningInteger

    DrowningInteger New Member

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    The two broken wires were branching off of the main dash harness a few inches away from the shifter.
     
    #31 DrowningInteger, Jul 23, 2025 at 5:46 PM
  12. DrowningInteger

    DrowningInteger New Member

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    Also I know I mentioned it seemed like at first that I had more issues when it was hot outside, but I'm not sure how much temperature matters. It worked fine for a week of 90-degree weather and then just quit working randomly on a 70-degree day.
     
    #32 DrowningInteger, Jul 23, 2025 at 5:51 PM
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