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2008 Prius, dead combo meter - battery kill switch fix?

Discussion in 'Gen 2 Prius Main Forum' started by Vae70, Sep 5, 2020.

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  1. Vae70

    Vae70 New Member

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    Hi Folks,

    I have an idea for a bit of a "fix" on my 08 Prius with the dreaded black combo meter defect. This first started occurring early last year, just out of the 10 year recall warranty period. I've dealt with it sporadically turning on/off for the better part of a year but now it seems to be prettymuch dead unless I manually pull the 2 plugs connected to the positive terminal of the auxillary 12v battery and re-seat after 30sec or so. While this workaround is generally successful, its annoying to do and runs the risk of permanent damage to the fragile battery connectors from constant pulling/pushing.

    I figure the root solve here is disconnecting the 12v battery power from the car somehow for a short while and a better way to do so would be to install a kill switch on the negative side (ground) lead coming off of the 12v battery. I'm hoping that rather than the usual use, the switch could be used to power-cycle the car, forcing the combo meter on while doing so. Ideally I'd run the 4 gauge wiring up near the driver's seat for easy access but if the length of wire or location is a problem I'd leave the switch in the rear hatch.

    Has anyone tried this to solve combo meter issues?
     
    #1 Vae70, Sep 5, 2020
  2. bisco

    bisco cookie crumbler

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    why not replace the meter?
     
    #2 bisco, Sep 5, 2020
  3. TMR-JWAP

    TMR-JWAP Senior Member

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    I figure the root solve here is disconnecting the 12v battery power

    You misunderstand the meaning of root causes and correcting them....:)

    Replacing the combo meter really isn't that hard.
    1. Contact Matt at Texas Hybrids and purchase a combo meter programmed with your mileage
    2. Remove the front panels from the dash
    3. Remove the lower and upper glove box doors and cavity.
    4. Remove the plastic covers from the window pillars
    5. There are two 12mm (?) bolts that thread into the passenger air bag from underneath. Remove those two bolts.
    6. Start prying up on the dash cover.
    7. Disconnect wires as needed while lifting up the dash.
    8. Once dash is loose, take it out of the car, flip it upside down on a large towel or blanket.
    9. Swap out the combo meter.
    10. Put it back together.
    11. Live happily ever after
    12. Or, next time you're in Texas, visit Matt at his shop and I think they do the swap for like $75 bucks or so if you buy the CM there..
     
    #3 TMR-JWAP, Sep 5, 2020
    donbright likes this.
  4. TMR-JWAP

    TMR-JWAP Senior Member

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    Has anyone tried this to solve combo meter issues?

    I've heard of taxi's doing it to cycle power to clear a P0AA6 HV Isolation fault. This fault will allow you to keep driving the car, but once you turn the car off, it won't let it go to ready state again. Cycling power clears the code and allows the car to work again.

    Same basic theory as what you want to accomplish. You could also just install a remote relay in the ground cable and just run small wires to an inconspicuous switch in the people compartment so the switch will open the relay to disconnect the ground wire. This type system has been used to kill power to the car as a theft deterrent also. You probably want the relay to be open when power is removed and apply power to close the relay, otherwise your 12v battery would drain holding the relay open with no way to recharge the battery.
     
    #4 TMR-JWAP, Sep 5, 2020
  5. Vae70

    Vae70 New Member

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    This is ideally what I'd like to do - the car is on its way out and I'm planning for a replacement early next year, the "fix" is just something that would allow me to check in on my fuel gauge every once in a while. Speedometer is handled on phone when I drive either way. Paying to replace the meter seems wildly expensive compared to just using a relay
     
    #5 Vae70, Sep 6, 2020
  6. donbright

    donbright Active Member

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    it is not guaranteed that disconnecting/reconnecting the battery will start the car. the components on the combo meter degrade more and more and eventually it will completely stop working.
     
    #6 donbright, Sep 7, 2020
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