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Weird Crazy Prius

Discussion in 'Gen 2 Prius Technical Discussion' started by JJ Pen, May 30, 2023.

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  1. JJ Pen

    JJ Pen New Member

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    Hey Y'all I have some codes that keep coming back after clearing twice with Dr.Prius app. Car has 240,000m. I have had problems in the past with smart key not working, car not unlocking but that was resolved with a new 12v battery. Last I checked the 12v battery was at 12.4v after a short drive sitting for 30m. I will try parking the car further away from home as some owners have shared here a close distance can drain the 12v. It seems like my car has covid. Different weird symptoms exhibit each day.

    First, Car threw red exclamation point and these codes, U0100 U0293 AFTER PRESSING CAR OFF BUTTON. Ran just fine with codes but didn't try driving on the road.
    Inspected HV fuses under the engine hood, they seem fine, have a voltimeter but don't know how to use it to test the fuses. put them back and it seemed like it reset the Hybrid code, only the engine 0293 was left so I cleared it and went on my way for about athousand miles,

    Then, few highway trips later again, AFTER PRESSING CAR OFF BUTTON, the same codes threw. car was driven a bit no problem. Left sitting for a week. DId the same procedure, checked all the fuses on the right compartment (remove, reinsert) fine, reset codes. I also reset the maintenance light. Another 300 miles later,

    Then 2 days later When trying to turn the car off, it freakked out. Turned off, but then came back on with no dash lights but the touchscreen on and engine running. Power button couldn't turn it off. Somehow my wife managed to turn it off and it drove fine without codes the next day.

    Finally, this morning, my wife couldn't get the keys to work, no smart key or fob lock unlock buttons would work. Battery 12v at 12.4v Eventually the car alarm went off, and she was able to unlock it.... and I drove it back home.... no problems yet...........

    I've tried looking on the forums for the codes but often there are no resolution to things. I've been doing more work so maybe I bumped something? recently put new fender liners on after a season of winter without them. dissasembled the dash to try and get the rear defrost to work, fuse was fine.

    Thanks for any help you can give!
     
    #1 JJ Pen, May 30, 2023
  2. JJ Pen

    JJ Pen New Member

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    I will try unplugging the 12V for a couple of minutes and see how that goes. I have techstream installed on a laptop... but haven't used it yet/before
     
    #2 JJ Pen, May 30, 2023
  3. JJ Pen

    JJ Pen New Member

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    I went to disconnect the 12V and I couldn't open the trunk because there was no power. I climed in through the window and was going to test the battery with my voltometer when all of a sudden the lights came on and the power came on... Any ideas on how to diagnose a loose battery connection? perhaps the cuts from the 12v is what is causing all of the problems? reverse beep I disabled came back on ;)
     
    #3 JJ Pen, May 30, 2023
  4. ColoradoBoo

    ColoradoBoo Senior Member

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    The issues may be related to a corroded/rusty ground somewhere...which can be a nightmare to locate. Start with the 12-volt battery ground(s) and get a strong flashlight and look at all the grounds you can spot.
    Does anyone have a diagram of ground locations for a 2004 Prius?
     
    #4 ColoradoBoo, May 30, 2023
  5. TMR-JWAP

    TMR-JWAP Senior Member

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    Your problems sound like they may be related to a loss of 12v power.
    Start with the basics. Your 12v battery is located in the trunk area passenger side rear. Make sure the terminal clamps are tight and the black wire connection to the car body is tight. Make sure the heavy cable and small wire are both securely plugged into the positive terminal fuse block.

    You could have someone hold your voltmeter measuring voltage at the underhood jump point while you wiggle the 12v battery cables around at the rear of the car. Any change in the voltage reading would tell you where the problem lies.
     
    #5 TMR-JWAP, May 30, 2023
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  6. edthefox5

    edthefox5 Senior Member

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    Do you get a Red Triangle on the dash?

    Does the car have the original hybrid battery and if so how is it doing? Not good I would imagine given its age.

    Where are you getting codes U0100 and engine 0293 from? Those are not Car OBD codes and are meaningless to this discussion.

    If your chasing 12 volt battery issues it only matters what you are measuring at the front jump point under the hood. Do not ever measure at the battery again.
    The front jump point is under the hood in the black fuse box on the right under the red plastic cover. Flip that cover up and measure DC from that jump point to chassis ground. I use the bolt right above it for the front strut as chassis ground. Works good.

    When testing at the FJP you are testing all the connections that have to be made from the battery in the trunk to the engine. Its like 8 different connections and a 100 amp fuse @ the battery and a long power cable before it gets to the front fuse box jump point before it can do some work. That's where you need to measure it.

    With the car off what's the battery measure at the FJP?

    And most 12 volt battery connection issue's are from the 12 volt battery negative ground post connection to the ground lug bolted to the body. That body bolt connection sometimes get loose or corroded where it bolts to the body.
    Has to be unbolted and sanded down there to fresh metal on the lug & body and apply lubricant and bolt back up.
    Beware: Many posters have over tightened that body bolt and stripped that body bolt hole. Its tough to get to and that's when people go all mungo on a bolt.

    This connection:.
     

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    #6 edthefox5, May 30, 2023
    Last edited: May 30, 2023
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  7. dolj

    dolj Senior Member

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    Those are OBD codes and are not meaningless. The "U" codes are communications error codes and the most common cause for loosing communications with an ECU is loss of power.

    Seems to be a common theme at this juncture.
     
    #7 dolj, May 31, 2023
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  8. JJ Pen

    JJ Pen New Member

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    Thanks for all the responses.

    I checked the 12v connecting cable and it was very loose. Tightened it and added where there was obviously a missing bolt. Hopefully that resolves the problem. If more problems, I will try what TMR-JWAP suggested and check the change in voltage around cables.

    Now the left brake light and left headlight have no power to them......
     
    #8 JJ Pen, May 31, 2023
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  9. TMR-JWAP

    TMR-JWAP Senior Member

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    Ta-ding!! Sounds like you found the problem!! Well done!

    It's crazy how often these 12v battery connection problems happen.
     
    #9 TMR-JWAP, May 31, 2023
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