2008 won't start after sitting for 2 weeks

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by PriusOwner428, Sep 17, 2025 at 8:03 PM.

  1. PriusOwner428

    PriusOwner428 Junior Member

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    2008 sat for 2 weeks while we were on vacation. Upon returning it would not start. Hooked up charger and connected charger cables to the positive post on the fuse panel in the engine compartment and a bolt for ground. Battery is reading 12.4V now, but ignition will not start. Dashboard display is completely dark and shows no life at all when the start button is pushed with the keyfob in the slot. But headlights, horn, cabin lights etc all work. Also, while completely dead, it does show the car door open red LED light and when the start button is pushed without the key in the car it displays the "no key detected" symbol. So the battery is working for all these items but it seems like the ignition has been disabled. Is there some major fuse or other disconnection point that might need to be reset?
     
    #1 PriusOwner428, Sep 17, 2025 at 8:03 PM
    Last edited: Sep 17, 2025 at 9:10 PM
  2. bisco

    bisco cookie crumbler

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    maybe the load on the 12v is too much to close the start up relays. how old is it?
     
    #2 bisco, Sep 17, 2025 at 8:07 PM
  3. Hayslayer

    Hayslayer Member

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    I don't remember all the details, but your symptoms sound similar to the AM2 fuse being open.
     
    #3 Hayslayer, Sep 17, 2025 at 10:34 PM
  4. PriusOwner428

    PriusOwner428 Junior Member

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    Right. And that was the first thing I checked. Visually it looked OK. Tested with a meter & it was good. Had a 6.8 ohm reading so replaced it with a new fuse for good measure. Didn't help.
     
    #4 PriusOwner428, Sep 17, 2025 at 10:52 PM
  5. PriusOwner428

    PriusOwner428 Junior Member

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    Not sure about age. Bought car used 2 years ago and have never changed the battery. But would the start up relays need more power than the headlights and horn?
     
    #5 PriusOwner428, Sep 17, 2025 at 10:56 PM
  6. dolj

    dolj Senior Member

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    There is a short but significant power draw during the start-up sequence. You need to monitor the 12 V voltage while starting up to ensure the car does not dip below 11 V while starting up. A low voltage condition during start-up can set codes that prevent the car from going READY.

    Before doing any diagnosis, you must confirm that the 12 V battery is in good condition and fully charged. If it is not in good condition, the battery needs to be replaced.

    You could also have a combination meter (CM) failure. See the Combination Meter Repair - DIY thread for details. The link will take you to a post detailing all the parts that Hybrid Texas Batteries (THB) replaces when they remediate a CM board. Most people can replace only the 110 µF/16V capacitor (replacing it with a 220µF/16V) and get lasting results. As people pay money and THB gives a lifetime warranty, they replace all the parts in the list.
     
    #6 dolj, Sep 18, 2025 at 12:08 AM
    Last edited: Sep 18, 2025 at 12:20 AM
  7. PriusOwner428

    PriusOwner428 Junior Member

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    OK thank for the detailed and thorough info. I'm lucky in that I have another 2008 Prius that is working just fine. So I will swap batteries and see if the problem follows the battery. When you say it could set codes that prevent the car from going ready, does that mean I now have to somehow clear those codes before trying again?
     
    #7 PriusOwner428, Sep 18, 2025 at 1:10 AM
  8. dolj

    dolj Senior Member

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    It depends on the codes. Some will clear themselves after some number of cycles of not seeing the problem again. Disconnecting the battery will also clear most codes, so if you have codes after that, you should really investigate those first, as in that case, you do have a real problem that most likely needs fixing before you can clear the codes.

    If you are talking about the 12V battery, I wouldn't swap it; I'd just charge it. But if you insist on swapping it, make sure you charge the spare battery (and load test it to confirm it is in good condition) before installing it in the car.

    Now that you mention clearing codes, if you have the CM problem, you will not see lights on the dash that indicate codes have been set in the corresponding ECU(s). If you do have codes, it would be best practice to read and record them before clearing them.

    Report any codes you currently have in this thread.
     
    #8 dolj, Sep 18, 2025 at 1:21 AM
  9. PriusOwner428

    PriusOwner428 Junior Member

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    Well the battery I would be swapping into the car with the problem is coming from a car that is working just fine right now. So the swapping battery is definitely good. However, I am currently charging the potentially bad battery over night in place. I disconnected the positive lead and placed the charger cables directly on the 12V battery. So it's charging over night for 8 hours. I will check with a meter in the morning to see what voltage it reads after over night charging. If it's 12V and above I will connect the positive lead in and try to start the car. I will do what you said and have someone connect a meter and see if the voltage drops below 11V during the start attempt. If it won't start I will then swap batteries and try with the known good battery in place.
     
    #9 PriusOwner428, Sep 18, 2025 at 1:48 AM
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