2008 Prius won't start, is it a Short? Dead 12v? Fuse? Something Worse?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by CommunityCommuter, May 28, 2021.

  1. CommunityCommuter

    CommunityCommuter New Member

    May 27, 2021
    Greater Seattle Area
    2008 Prius
    Bought this car 4 weeks ago*** & is my first prius. Problems started 10 days ago.

    10 Days ago: I get to my Prius after its parked overnight and doors won't unlock with smart key, (Driver door unlocked but doors closed) Dashboard lights not on, dome lights do not come on. After about 15 mins of getting in and out of car, looking for anything obvious under the hood, trying to open back hitch, calling roadside assistance... the light on the Power button became orange, and I sat in the drivers seat and the car started up normally. Except the Trip odometer & Consumption stats were reset, and the clock was reset to 12:00

    2 days ago: I get back to my car after its sitting in a parking lot for an hour. The dashboard lights light-up as I get in, and by the time I press the Power button, all the car is dead, no lights. After waiting 2 mins and opening the doors, I try the Power Button again, and it works, car starts. This time the clock is reset set to 1:00, and the Last Empty fuel bar is flashing like there is low fuel. (While the fuel was recently on its last bar once I parked, I was not at low-fuel).

    Today: I get to my car after it sits in a parking lot for 2 hours. (Doors unlocked & Closed). The dashboard lights light up. By the time I'm seated & press the power button I can't start the car, dashlights are off. The light on the "Parking" button pulsed green & the dome lights are very dim & the smart key missing symbol pops up momentairly, then everything black. We try looking at everything, seeing the fuse box, opening & closing doors. Nothing else ** . We jump the Prius using a battery starter pack (shout out to the Prius Chat community for helping us avoid destroying the whole car), and the Headlights turn on immediately. Power button glows orange, no starting, and the headlights dim rapidly. We do this 2 more times, conserving by turning off the headlights. Dashboard lights came on each time, yet car wouldn't start. By that point we spent the whole battery, and decided we would start again in the morning.


    ** I am not sure because I forgot to take a picture, but a 7.5A Fuse in the engine compartment fuze box, potentially "OBD" was missing.

    *** Recently purchased Prius 2008, Perfect Maintenance History from Toyota Dealerships, every 5000 miles, through 116k. Last record 2019, since, there has been 2k miles put on, in past two years.
  2. rjparker

    rjparker Senior Member

    Jun 6, 2008
    Texas Hill Country
    2012 Prius v wagon
    Did you measure the 12v battery? Odds are its bad. So bad that a jumpstart has a hard time bringing the voltage up enough to run.
    audiodave and SFO like this.
  3. sam spade 2

    sam spade 2 Senior Member

    Mar 31, 2018
    2017 Prius c
    Odds are GREAT.

    Second most likely cause: Loose or corroded main battery cable connections.

    Or a combination of both.
  4. audiodave

    audiodave Active Member

    Feb 3, 2017
    2004 Prius
    Try charging and cleaning 12v first.
    Posted via the PriusChat mobile app.
  5. JohnPrius3005

    JohnPrius3005 Junior Member

    Feb 4, 2021
    California and Hawaii
    2004 Prius
    I suggest from experience you disconnect the 12V bat. You can do that by either removing the negative terminal from the negative battery post, or by unplugging the large white plug from the positive terminal connection (I'm not 100% sure your 2008 model has this large white plug, so if you don't see it, just remove the negative terminal instead). Disconnecting the battery will clear some codes and reset various things - like programmed radio stations - but these may have already been lost by your 12v bat getting low.

    Now charge the 12v bat with any normal battery charger. It may be best to leave it charging overnight. Most battery chargers will start at 10 or 5 amps and revert to "trickle" charging at 2 amps once the battery gets close to being fully charged. Some battery chargers will indicate that this has occurred and give you a green light that the bat is good, or an indication that the bat is bad.

    Disconnect the charger.

    Reconnect the negative terminal (or reinstall the big white plug).

    Get in the car and do what you normally do to start it. It probably won't start and many warning lights will come on, fuel will show zero, etc. Wait about 30-45 seconds. With your foot still on the brake, push and release the power button again. The car will likely start.

    You probably have a bad 12v bat.

    Of course instead of all the above you could just install a new 12v bat right away.

    If you want to keep using the car prior to replacing the 12v bat, and you have a secure garage to park in, you can repeat the above process. Leave the "trunk" open with an old 2x4 to allow you easy access once the bat is disconnected. It's a little more complicated if you don't have a secure place to park, and you'll need to use the metal key to open the door, and crawl into the back to get to the bat/open the "trunk".

    Good luck. ;-) These cars are a helluva learning experience!!