Which Computer Is Slow To Boot?

Discussion in 'Generation 1 Prius Discussion' started by Brock Turner, Jul 13, 2026 at 2:40 PM.

  1. Brock Turner

    Brock Turner Junior Member

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    Location:
    St. Paul, Minnesota
    Vehicle:
    2002 Prius
    Model:
    N/A
    This morning was the second time this happened. Both times were 'cold' starts when the outside temp was above 90F

    It took about 30 seconds once the TOYOTA screen went away for anything to appear on the screen, then...

    DSC_0920.JPG
    This is the energy monitor with car in READY, and driving about 20mph

    DSC_0921.JPG
    The consumption screen at this time was pegging at EV/infinite MPG at any speed over 5mph

    DSC_0922.JPG DSC_0923.JPG
    A few blocks later (3-5 min) all is well with the consumption and energy screens.

    Other things...
    • The battery fan was not running at take off, but came on at a very low speed after about 15min the first time this happened.
    • No turtle light or codes, (which would tell me the battery itself is probably not the problem??)
    • If memory serves... this happened at least once before when temps were in the -25F range (too cold to document :confused:)
    • AC was blasting when the symptoms went away, that makes me think it could possibly be the Gateway overheating (since I'm 80% sure it is sandwiched under the screen between the major AC vents)
    • Mileage and running of the car has been/is phenomenal, I routinely average 48-54mpg on a 3 year old refurbished Greentec battery, and the engine is so quiet and smooth I can't feel when it comes on/off when driving around town.
    • 335,XXX Miles :whistle:
    Thanks in advance for any help !
     
  2. Trombone

    Trombone Active Member

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    Location:
    Allentown, Pennsylvania
    Vehicle:
    2002 Prius
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    Above 90 in St. Paul?!! In the morning yet? My sympathies.

    Your gateway theory might be on target. My screen is dimmed out on very cold mornings (in s.e. PA that means below 32ºF) until the cabin heat comes on for a few minutes, then it's fully functional. Solder connections don't like extremes, I guess. In temperate seasons (IOW, not winter) the screen works fine.

    That's indeed fabulous mileage! I have a greentec with "new" cells in my '02 (178k miles) but my mileage stays down in the 40s around town.
     
  3. Brock Turner

    Brock Turner Junior Member

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    2002 Prius
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    Thanks for your reply!

    It seems the Gateway ECU is pretty inexpensive and would be easy enough to change if the problem persists. Out of curiosity I checked the state of my Optima Yellow Top 12v, and it seems to be healthy enough.

    I should have added an asterisks to my mileage. That is only when I TRY for mpg outside of winter. Interstate, winter cold starts, and other drivers bring it into the mid 40s.

    The biggest factors for upper 40s-low50s for me, are keeping the AC on Auto 78F, tire pressure 48psi, avoiding stop LIGHTS, and keeping the battery full by using heavy regen (which allows the car to accelerate to 12mph as opposed to 8mph at every intersection) and avoid using the battery for any acceleration by keeping the same rate of acceleration when the ICE fires up (very constant and slow). I also switched to 5w-20 and 0w20 depending on the season (not in the manual, but 5w-20 is listed as an acceptable oil for the nwh10/11 in Japan and 5w-20 seems to have been retroactively approved by Toyota US according to an oil weight by model chart I've seen at my dealership), which has increased interstate and highway milage by about 3mpg very consistently.
     
    #3 Brock Turner, Jul 14, 2026 at 5:14 PM
    Last edited: Jul 14, 2026 at 5:19 PM
  4. Trombone

    Trombone Active Member

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    OK, not sure I understand what you are referring to as the Gateway ECU.Tell me more!
     
  5. Brock Turner

    Brock Turner Junior Member

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    2002 Prius
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    N/A
    I'm sure there are people here who maybe no longer own a Gen 1.5 who could explain it better than I can, but...

    DSC_0925.JPG DSC_0926.JPG
    It's this little bity black box located under the hazard button, easily visible by just popping that out.

    DSC_0927.JPG
    My car has been parked under a tree in the shade all day (high of 96F) it's currently about 88F where I am, and this box reads about 102-4F with the car off.

    DSC00314.JPG DSC00313.JPG
    From what I can decipher from the wiring diagram... the Gateway ECU takes inputs from the HV ECM, ICE ECM, Navigation System, Radio Amplifier (tape deck), and the Auto AC amplifier for some reason (maybe just to display the outside temp in the corner?)

    My theory for this Gateway ECU being the problem, is the fact that this seems to be the intersection of data visible on the screen. Also, given there are not OBD2/Techstream codes, or any running issues I doubt it has anything to do with the HV ECM or ICE ECM.