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I cannot get my Prius to Start!

Discussion in 'Gen 2 Prius Main Forum' started by Prius92, Oct 3, 2024.

  1. Prius92

    Prius92 Active Member

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    Location:
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    Vehicle:
    2008 Prius
    Model:
    II
    I keep getting P0122, P0222 and P2315. Which results in P0A0F "engine failed to start".

    All related to the throttle position sensor.

    I've taken the relevant harness out of the ECU and the throttle position sensor, and probed all corresponding wires, the resistance is perfect, there are no cracks or anything in the wires.

    There are no codes coming up for the throttle control motor. However, it is my understanding upon putting the car in "ready" mode, the ECM should move the throttle back and forth a couple times. This isn't happening.

    There is no voltage going to the throttle control motor upon putting it in "ready" mode.

    This is what the workup says :

    "When malfunction is detected, the throttle valve is locked at a certain opening angle. Also, the whole
    electronically controlled throttle operation is canceled until the system returns to normal and the power switch is turned OFF"

    The issue I am having, is the 3 DTC's come on as soon as the car is turned on. Removing the battery cable does not seem to clear them.

    Here is where it gets tricky.
    The workup for the DTC's shows the VC power coming from a singular ECM connector with the other wires coming off it as well.

    [​IMG]

    BUT the master wiring manual shows VC coming off "Junction Block Connector J14".
    [​IMG]

    I'm stumped. I tried changing out the throttle body with a replacement and it did no good.

    There's 4.7v at the throttle position sensor.

    Could I possibly somehow have a bad ECM?
     
    #1 Prius92, Oct 3, 2024
  2. pasadena_commut

    pasadena_commut Senior Member

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    Probably not the issue, but check that your 12V is still good. These cars do odd things when it is too weak.
     
    #2 pasadena_commut, Oct 3, 2024
  3. ChapmanF

    ChapmanF Senior Member

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    You might want to check this post for some of the lay of the land.

    That doesn't have to stump you. VC is an output from the ECM: it is the 5-ish volt supply to the throttle position sensor, and evidently to a couple other sensors that also like a 5-ish volt supply, so it gets split up at J14 and sent to them too.

    The two signals that are unique to the throttle position sensor are VTA1 and VTA2, coming from the sensor back to the ECM.

    The codes you've got are telling you:

    • VTA1 has been seen 0.2 V or less for at least 2 seconds (the healthy reading should never be that low)
    • VTA2 has been seen 1.75 V or less for at least 2 seconds (the healthy reading should never be that low)
    • VTA1 and VTA2 have been seen not in the proper relationship to each other (the proper relationship is shown in a graph in the post linked above)

    With that information and some basic elec troubleshooting, it should be possible to pin down why.
     
    #3 ChapmanF, Oct 3, 2024
  4. Prius92

    Prius92 Active Member

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    2008 Prius
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    Well I figured it out. At one point in time someone took the throttle body apart.

    The arrangement of the throttle position sensor is super sensitive. I'm not sure why they made these adjustable as per the FSM, there "is no adjustment". It's really a goofy setup.

    I tinkered with it and now it does run.

    Funny thing is, per the DTC workup, it's at least supposed to go into a limp mode so you can get home, but apparently not...
     
    #4 Prius92, Oct 3, 2024
  5. ChapmanF

    ChapmanF Senior Member

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    Limp mode might depend on whether the condition is detected while you're already driving, or right away before you've gone anywhere.
     
    #5 ChapmanF, Oct 3, 2024
    Brian1954 likes this.
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