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MFD Display check of 12V Aux Battery

Discussion in 'Generation 1 Prius Discussion' started by sandy11246, Jan 16, 2018.

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  1. sandy11246

    sandy11246 Member

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    Does anyone know where the information comes from displayed on the MFD regarding 12V battery voltage. When the MFD is used to check 12V battery voltage, what sensor or module sends that information to the MFD. When I run this test, there is a 0.8 volt difference between what is displayed on the screen and what my Fluke 87 III displays when it is connected directly to the battery terminals. I realize there can be some voltage drop do to connector or line resistance but I think 0.8 volts seem excessive. Any assistance on this would be appreciated. This is a 2003 high mileage Prius, so some circuit issues are anticipated. Just trying to clear all possible area as I precede with this project. Vehicle is still operating. Had 1 hick up over the weekend but cleared codes and all seems well.
    Also wonder if anyone considers low ICE operating temperature (135*F) might affect CAT operation. Feel it will and once had a P0420 (CAT out of parameters), but cleared it and no return. I am planning on blocking the radiator this week (Temps low here)to see how that works out. Will keep all posted on my project as it continues. Thanks to all. Peace
     
    #1 sandy11246, Jan 16, 2018
  2. padroo

    padroo Senior Member

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    #2 padroo, Jan 16, 2018
  3. ChapmanF

    ChapmanF Senior Member

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    That's roughly the same difference I've noticed, so I wouldn't worry about it. The MFD is simply measuring the voltage at its own terminals, which are downstream of the battery by at least one fuse link and at least one lower-capacity fuse, and you can only use it in ACC or ON, when other loads are also dropping voltage over those circuits. You may notice the difference ls smaller in ACC and larger in ON. (It can also be more variable in ON, because a wider array of other things may be drawing more or less power.)

    As long as you know about it, it isn't a problem for anything, though confusion sometimes reigns on PriusChat when this reading is reported and people apply right-at-the-battery voltage-to-battery-condition criteria to it.

    -Chap
     
    #3 ChapmanF, Jan 16, 2018
  4. sandy11246

    sandy11246 Member

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    Vehicle:
    2003 Prius
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    ----USA----
    Thanks Chap. I traced the voltage today to the HV ECU fuse and others in the engine compartment fuse box. Weather here has been single digits for a few days and voltage was lower than I hoped. Vehicle seems to operate normal, but twice in the last month had codes. Think the last set was triggered by a CAT parameter out of range. Am wondering if low operating temps are causing this because of very cold wx. Engine was 134*F during commute when code tripped as per “freeze frame”. Engine on time was 267 (4.4 minutes) Most vehicles reach operating temp within 5 minutes. Am going to block radiator this week and record results. Will also look into thermostat issue. Again, thanks Chap, this is a learning project for me. All advice appreicated.
     
    #4 sandy11246, Jan 17, 2018
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