yet another thermistor hack for Gen3

Discussion in 'Gen 3 Prius Accessories and Modifications' started by ken1784, Feb 25, 2010.

  1. ken1784

    ken1784 SuperMID designer

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    Hello all,
    This is another thermistor hack for Gen3.
    Warning: This modification may damage your cold engine.
    Warning: Toyota may void your Prius warranty for this mod.
    Warning: Please do it at your own risk.

    circuit-1: a simple solution. You do not need to cut any wire. Just connect a switch, 5k ohm variable resistance and 470 ohm fixed resistance.
    When the switch is off, the thermistor works as original, no modification.
    When the switch is on, the resistance value to the THW pin becomes combined value with the original thermistor and manual resistance value.
    We only can reduce the combined resistance value (set higher engine coolant temperature than real one) on this simple solution.

    circuit-2: a complex solution. You have to cut the original THW wire.
    However, You can fake any coolant temperature as you like.
    When switch to true position, the thermistor works as original, no modification.
    When switch to fake position, you can let the ECU know any temperature you like.

    The engine ECU is located under the hood, and the ECU connector is covered by plastic one.
    It is little tricky to remove the plastic cover. We have to push in two latches to remove it.
    Please refer to attached pictures.

    I am not intend to write how to use it and what kind of benefit we can get from this mod.
    If you don't know them, this is not for you. :)

    Enjoy,
    [email protected]

    [​IMG]

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  2. hobbit

    hobbit Senior Member

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    Has anyone with a fakeout found that when the engine *is* fairly
    cold and you fake it up close to stage 4 range, that it runs
    really *badly* at first? The ECM depends pretty heavily on that
    number, it seems, and these days I don't try to fake it from
    dead cold anymore but just help it get to 70C a little sooner.
    .
    _H*
     
  3. ken1784

    ken1784 SuperMID designer

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    I don't think the ICE runs *normally* with a fakeout when the engine *is* fairly cold.

    [email protected]
     
  4. TheForce

    TheForce Ron Paul 2012

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    I have found on my Gen2 that if you start faking when the temp is below 100F you start to have engine problems. Lots of stuttering. Simple solution is to let the Prius warm up to 100F and then start faking.

    My/JSTCD's automatic temp hack will only start faking when the temp reaches 100F

    The only downside to my design is that it wont stop faking if the actual temp drops below 100F
     
  5. pablovv

    pablovv Junior Member

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    With this hack, setting the refrigerant fake temperature below 55C and activating the climatizer setting the temperature to max and the ventilation to min you can force the recharging function, right?
     
  6. mite66

    mite66 Junior Member

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    I installed mine yesterday and this hack is just perfect for someone that has a plug-in kit like Enginer's or other.

    On my dashboard along with Enginer's switch:
    CTH switch close-up.jpg

    My ECU connections:
    P1150256.jpg

    Details of my switch:
    Rear switch close-up.jpg

    The ohm values specified by Ken seem just perfect for my needs.

    Thanks so much ken1784 :rockon:
     
  7. mite66

    mite66 Junior Member

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    Well actually, my car sat for a couple of hours outside at -5oC today and when I came back and started it with the hack on, the highest temp I was able to get was 69oC. So not able to get my full EV mode.

    I will change the 470 ohms resistor for a 430 ohms and see if it works better for me.
     
  8. rrolff

    rrolff Prius Surgeon

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    Can someone explain what this does? Does it allow the car to run EV even when the engine is 'cold'?
     
  9. mite66

    mite66 Junior Member

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    Exactly, it makes the car think that it has already reach 70oC, even on your first start, and will therefore allow you to run full EV (up to 40km/h) right away.

    But again, this makes more sense only for cars that are equipped with PHEV kits.
     
  10. rrolff

    rrolff Prius Surgeon

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    Not sure - we have a few short drives (.8 miles taking kids to school - stop and go for a portion) - the darn thing runs most of the way, and by the time you get back, it stops (heated up).

    For this type of driving, maybe it makes sense....
     
  11. mite66

    mite66 Junior Member

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    If your total drive is .8 mile, than probably. You'll need to start with 6 bars though and you'll probably end up with nothing. So the next time you'll take your car for a longer run, the engine will run a bit harder just to charge up the battery, but overall, you'll probably save fuel compared to having it running like what you described.
     
  12. mite66

    mite66 Junior Member

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    Well I finally decided to go for a 330 ohms for more margin and it now allows me to reach the magic 70oC even when it's -10oC outside.:)
     
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  13. spiderman

    spiderman wretched

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    Amazing. So will using the heater circumvent the hack? Or does it just run cold?
     
  14. rrolff

    rrolff Prius Surgeon

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    What is the purpose of the variable resistor - does that mean you need to also be monitoring the car (via Scan*** or whatever) - and need to constantly change a pot to keep the car 'going'?

    TIA
     
  15. mite66

    mite66 Junior Member

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    Not really, It's all new to me but I'm pretty sure that the pot only need to be adjusted upon startup. And yes, a Scan*** is mandatory in this case.

    This is how I'm using it so far:

    ex. middle of winter
    1- Coolant temp 0oC
    2- Pot adjusted to present, say 75oC to the car
    3- Car is started, I ride EV all the way in city streets (PHEV shines here)
    4- I decide to go on faster streets so I make a complete stop (red light), cut off the hack and let the engine do its normal starting warm-up (because the ICE is still dead cold)

    So I normally never touch the pot.

    Of course, if I did a ride where the ICE was used and then stop the car for a while. When I'll get back in it to do some pure EV for a moment, the coolant temp may be at something like 45oC, so yes, I'll need to adjust the pot so that it won't create an overtemp situation.

    Also, my pot setting during summer time will also be different for the same reason, but again, it won't normally need to be touch.
     
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  16. mite66

    mite66 Junior Member

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    Heater ? what heater ? :crazy:

    The toque, scarf and gloves are mandatory equipment for a real winter EVier.:smow:

    I only run the heater when I do some highway and my real coolant temp has reached 70oC... mmm... only when the wife is not aboard that is :rolleyes:.
     
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  17. spiderman

    spiderman wretched

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    I'll take that as a yes.
     
  18. mite66

    mite66 Junior Member

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    Well the real answer would be:

    1- Heat comes from the engine.
    2- I don't turn on the hack when I'm using the engine.
     
  19. nerfer

    nerfer A young senior member

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    With his stop and go it may not drain the battery, if he turns it up whenever he's decelerating or stopped, and then drops the temp back down again when accelerating. Even though I don't have a PHEV I could use something like this on my long downhill to work when I'm typically at 145'F - 155'F this time of year.

    But 0.8 miles Rolff? Really? You can walk that distance in 15 minutes, why even bother with a car? Really! (Imagine a Seth & Amy imitation). Must be all that terrible weather you get in So. Cal. And doctors wonder why we don't get enough exercise in America.

    (BTW, I thought you guys weren't going to explain why this hack is useful, according to the PO)
     
  20. cproaudio

    cproaudio Speedlock Overrider

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    Anyone besides Mite did this mod? I'm thinking of using circuit 2 to get total control.
     
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