Prius won’t power on

Discussion in 'Gen 2 Prius Technical Discussion' started by Toddwilks, Oct 7, 2020.

  1. Toddwilks

    Toddwilks Active Member

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    2009 Prius 83000 miles car won’t turn on. 12v was replaced 4 months ago and won’t turn on when jumped.

    Dome lights work
    Headlights and fogs work

    No lights on dash, no orange red or green light on power button, no mfd display.

    12v replaced
    Power button replaced
    Trans computer replaced
    Power computer replaced
    Integration relay replaced

    When pressing the brake pedal, no brake lights come on at all.

    Pulled the cables from the 12v for over an hour to clear anything and same result.

    Could this just be a bad stop light switch? What else should I try?


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  2. TMR-JWAP

    TMR-JWAP Senior Member

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    Dome lights/headlights/fog lights at least means the power path from the 12v battery to the underhood jump point is good. The underhood jump point threaded stud is part of the main fusible link (the "white plastic box with the clear cover) It has several individual fusible links inside it to distribute power to the remainder of the fuse box. Are all the fusible links intact?

    Power computer=Power Source ECU?

    Safe to say that you've already verified all fuses in the under-hood fuse compartment?
     
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  3. jerrymildred

    jerrymildred Senior Member

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    If it was the brake light switch then, when you try to start it, it would go into ACC or ON, just as if you hadn't depressed the brake pedal. And that would turn on various dash lights. So, no I don't see how it could be the brake light switch.

    Saying the 12V was replaced 4 months ago is completely irrelevant. It could have been replaced in the morning and be dead the same afternoon under the right (wrong?) conditions. I'd guess it's OK though since the headlights work. I'd measure it anyway.

    The first thing I'd look at after verifying the 12V battery is reasonably charged up is the fuses. You didn't say if you'd jumped it or not. If you did and did it wrong, that would be the source of some blown fuses for sure ... and maybe much worse.
     
  4. Toddwilks

    Toddwilks Active Member

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    I did not check all the fuses. Car is at the dealer. Here is what they did
    IMG_0096.png


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  5. Toddwilks

    Toddwilks Active Member

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    The car won’t go into acc or on. It doesn’t recognize when the brakes are applied. I did mention jumping it and it won’t start after trying to be jumped. This is a very sporadic thing. Sometimes it starts right up, other times it’s completely dead like this.


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  6. jerrymildred

    jerrymildred Senior Member

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    So they're just guessing? I hope you don't have to pay for all those parts that didn't fix it.
     
  7. Toddwilks

    Toddwilks Active Member

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    I did not. Bought it like this from them. After reading everything I thought it was the brake light switch but want other opinions. It made sense to me since it won’t recognize the brake being applied at all.


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  8. SFO

    SFO Senior Member

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    Failed combination meter (dash) ?
     
  9. Toddwilks

    Toddwilks Active Member

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    That would cause the whole car not to power on? I didn’t think it was that because it’s sporadic. When it went out on my 07 I was still able to get the car into ACC or turn it on, I just couldn’t see anything.


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  10. TMR-JWAP

    TMR-JWAP Senior Member

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    For the entire car to not power up, other than head lights and dome there must be a significant issue. Hopefully, it's safe to assume the dealer properly replaced the items they say they replaced. There are several heavy gauge wires that bolt to the sides of the main fusible link. Obviously, they're not visible unless the link is lifted out of the fuse box. There's also 3(?) large, multi wire plugs that insert into the bottom of it. If any of these are loose, I would suspect it to cause serious 'no power' problems, very likely intermittently.

    Even if the car wasn't recognizing the key, it would still provide a warning light when the power button was pressed, so key recognition should be eliminated from being a problem.
     
  11. fotomoto

    fotomoto Senior Member

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  12. Toddwilks

    Toddwilks Active Member

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    Would a defective fusible link cause the car to sporatically turn on and work as normal and be completely dead some others?
     
  13. mr_guy_mann

    mr_guy_mann Member

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    If I had to look at this car then the first thing I would do is go through both fuse boxes and test for voltage with a DVOM at every fuse and write down the results.

    Then I would get wiring diagrams for the car and see what fuses are supposed to have constant battery power. Does that list match the results from testing the car?

    It sounds like there is power missing somewhere. You need to confirm this (or not) before you can form your next step.

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  14. TMR-JWAP

    TMR-JWAP Senior Member

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    Todd,

    The main (+) power cable from the 12v battery connects directly to the underhood jump point. It connects nowhere else and supplies power nowhere else. That underhood jump point is actually part of the main fusible link assembly (the white plastic part with see through cover) that's on the left side of the underhood fuse box. That assembly has several fusible links under the see through cover. Think of it as 12v power being connected to the head of an octopus, and each of the Octopus legs are individual fusible links. At the end of each leg, one or two heavy wires are bolted to it. Each of those wires supplies a circuit in the fuse section of the fuse box. If any of those bolts are loose, that circuit is going to have intermittent problems. Everything in your car that gets 12v power, gets it via that fusible link assembly.
     
  15. TMR-JWAP

    TMR-JWAP Senior Member

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    In this photo, you can see the jump point stud. There are two main power busses, with one on each side running the length of the plastic box. There are several individual "fusible" thin metal branches that drop down from each bus. Directly below some of those 'drops' is a threaded connection where a bolt fastens a cable. The drops that don't have threaded fasteners have a plug that inserts upward from the bottom and clicks into place. Those cables then supply the various branch circuits. The 'fusible link' that is circled is the one that blows when a reverse jump is performed. I just happened to grab this photo from my files.

    Fusible Link.JPG
     
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  16. Toddwilks

    Toddwilks Active Member

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    This is all good stuff. I’ll look into this further and report back. Is there a how to on removing this part to check the connections under it or to replace it?


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  17. Toddwilks

    Toddwilks Active Member

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    Confirmed with autozone and Napa the 12v is good. Waiting to try and start it again and will be bringing it to the dealer to diagnose. Fusable link looked ok, no loose bolts or wires and fuses looked good


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  18. Toddwilks

    Toddwilks Active Member

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    Spoke to the dealer yesterday, turns out there is a short within the dash wiring harness. They recommended replacing the entire dash harness for a ridiculous amount. I called Toyota to see if they can do anything about it or help out since it’s not really a common problem. We will see what happens.


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