2005 Prius dying/resetting/malfunction?

Discussion in 'Gen 2 Prius Main Forum' started by clamx, Jul 20, 2020.

  1. clamx

    clamx New Member

    Joined:
    Jul 20, 2020
    2
    0
    0
    Location:
    Idaho
    Vehicle:
    2005 Prius
    Model:
    ----USA----
    Okay, I’m not sure how to explain this... we replaced my 12v battery recently and everything was working great for a while but then I got in and my car was completely dead (no lights or signals of ANY kind working). I thought it had to be jumped but when I took the key out and put it in a few times, it started just fine- but everything was reset. My miles, radio presets, temperature, everything. Every time I start my car now it does that same thing. Radio on a random station, A/C on 75* (even if they weren’t on before my car turned off). Sometimes it’s dead/off when I try to start it and I can open and close my door, etc. to get it to start again.
    Now it’s doing more weird things. I have to put my key fob in to start it, but sometimes when I turn the car off and take my key out the car starts by itself! Like all the way. I can’t start it without the key in the slot, so I have no idea what’s going on. Today I got in and shut the door and the car started all the way up. I was so confused and I decided to see if it would drive and it does, I went all the way to work. Then when I turned it off it wouldn’t start again. So weird. Does anyone have any clue what would cause this? We checked my battery connection, etc. but I’m not sure what else to look at/why it will start without the key in and without hitting the power button. Help? Thanks in advance.
     
  2. PriusCamper

    PriusCamper Senior Member

    Joined:
    Mar 3, 2012
    5,643
    2,290
    0
    Location:
    Pacific Northwest, USA
    Vehicle:
    2007 Prius
    Model:
    Two
    This is a known problem... I have it in my 07 and it never sticks around long enough for me to do a full diagnosis... But essentially what going on is related to the shut down sequence of all the relays when you turn your car off. And for some reason when some of the connectors with the 12v battery don't get all the way tightened, or possibly damaged, the car's final sequence of shutting down gets screwed up.

    For my 07, if you stare at your combination meter (mph, miles traveled, gear position, guess gauge) when shutting the car down, the last light to go out is the gear position section on the far left. But if that side goes out at same as the rest of the dash, the shut down failed and the car loses all accessory power, radio presets, trip meter, etc. Then most of the time after I'm done freaking out the problem goes away. Or if I right away open and slam shut my right rear door real hard the problem fixes itself without losing radio presets, etc..

    And yes the worst is when I get out of my car not realizing it got screwed up again and then the car re-starts in diagnostic mode even though there's no key fob in the slot or inside the car...

    If this starts acting up for me again, I'm going to take apart all the devices that attach to the 12v for a thorough cleaning and inspection to see if I can learn more, or find physical evidence of the point of failure. I suspect this one will fix itself by getting everything cleaned up and tightened, but not sure yet because it's only been a problem every half year or so...

    I wonder if @Patrick Wong or @Mendel Leisk or other folks who've been around longer than I know more about Prius shut down relay sequence?
     
    clamx likes this.
  3. clamx

    clamx New Member

    Joined:
    Jul 20, 2020
    2
    0
    0
    Location:
    Idaho
    Vehicle:
    2005 Prius
    Model:
    ----USA----
    Thank you! That’s all really good to know! :)
     
  4. dolj

    dolj Senior Member

    Joined:
    May 14, 2012
    5,289
    2,853
    0
    Location:
    Wellington, New Zealand
    Vehicle:
    2007 Prius
    Model:
    N/A
    Your description sounds like there is a loose connection at one or both of the battery terminals.

    When you replaced the 12 V battery, did you use a screwdriver between the lugs (where the tightening bolt goes through) to widen the post clamp so that it slides snuggly right down to the bottom of the terminal post? You need to do this on both the positive and negative terminal posts. You then use a box wrench or a socket wrench to do the bolt up. This avoids the tendency to lever the clamp up off the seat of the terminal post, which is prone to happen if you use an open-end wrench. When you have tightened both terminal bolts, give them a good wiggle and ensure they are snugged tight. Next, have you checked where the negative cable attaches to the car body? Is it clean and tight?, If not clean it up and tighten it.
     
    Prodigyplace likes this.
Loading...