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  1. black_jmyntrn

    black_jmyntrn Senior Member

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    In Techstream, what is the significance of these highlighted items, trying to make sense of why the engine does not start and hoping someone can shed some light for me.
    I've been troubleshooting a persistent issue with my grey Generation 2 Prius ever since I purchased it from a tow truck driver for $1,200 shortly after my accident in January 2023. The car had been sitting for nearly a year due to registration and operability issues, and I’ve been working on getting it back on the road for the last few months.

    Recently, I've been dealing with error codes that have been particularly challenging to diagnose and resolve. The primary issue seems to be centered around the P0A0F/204 error code, which indicates an "Engine Failed to Start." Additionally, I received the P0125 error code, related to the Engine Coolant Temperature Sensor, and P3190, which indicates "Poor Engine Power."

    The car shows symptoms where the RPMs gradually increase for about 10 seconds after starting, and then it shuts off, triggering a red triangle warning light. The engine doesn't seem to rev up properly when the gas pedal is pressed, which led me to believe that the throttle position sensor might be the culprit.

    I've tested and replaced several components to pinpoint the issue:

    1. Throttle Position Sensor: I initially replaced the throttle position sensor with one from a dismantler, but the issue persisted. The RPMs kept climbing without regulation, and the engine still failed to start properly. I recently cross-referenced Toyota part numbers and found a throttle position sensor at AutoZone that matched my research. However, even this new sensor didn’t align with the specifications outlined in the Toyota Tech documentation I have. The readings from this new sensor were also out of spec, leading me to question whether the issue lies elsewhere.

    2. Engine Coolant Temperature Sensor: Since the P0125 code pointed to a problem with the engine coolant temperature sensor, I checked the resistance and manually bled the system again, hoping to resolve the issue. However, this didn’t make a significant difference in getting the car to run.

    3. MAF Sensor: I also checked the MAF sensor by taking it off and testing it with some power to ensure it wasn’t the problem. The MAF sensor checked out fine, which left me more convinced that the throttle position sensor or something related to it was the root cause.
    Despite all these efforts, the car still refuses to run properly. I'm beginning to suspect that there might be something more fundamentally wrong with the vehicle. The throttle body and sensors I replaced had markings from a dismantler, which could indicate that someone else had already tried to fix this issue before and failed. This makes me wonder if there’s a deeper problem with the car's electronics or some other component I haven’t yet considered.

    The frustration lies in the fact that no specific error code is being thrown to indicate precisely
    [​IMG]

    any guidance is appreciated.
     
  2. ChapmanF

    ChapmanF Senior Member

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    In each of those freeze frames, the actual engine torque is negative, meaning MG1 is still doing the cranking. The cranking has been going on for 14 or 15 seconds, and by that time the ECM estimates the engine ought to be producing around 56 Nm of torque, which isn't happening. Over seven seconds have gone by with the ECM hoping to judge that ignition is happening, but no such luck.

    The target cranking RPM is 800, which doesn't seem unreasonably high, but the actual engine RPM seems to be scrolled out of your screenshot.

    The engine doesn't rev up as expected when the go pedal is depressed because it hasn't got any 'go' to give; the negative actual torque reveals that it still is just being cranked.
     
  3. black_jmyntrn

    black_jmyntrn Senior Member

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  4. black_jmyntrn

    black_jmyntrn Senior Member

    Joined:
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    Location:
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    2013 Prius Plug-in
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    Plug-in Advanced
    here are the others I grabbed with the first image I posted
    20240808_191448.jpg
     

    Attached Files:

  5. ChapmanF

    ChapmanF Senior Member

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    The "does this help any?" image doesn't help much, because those values seem to have been stored at a moment nothing was happening; the RPMs are all zero.

    In the other images, the ones that show the actual engine RPM from a P3191 show it closely matching the 800 RPM target from the earlier image. It doesn't look like there is anything unregulated about the cranking speed.

    That last screenshot, taken from the HV control ECU, shows a different RPM of 1280. That's different from the ECM's 800 target (but not really different from the initial RPM that I typically see right when my engine starts, so it still doesn't seem unregulated/implausible).

    Not being there with hands on, I don't think I have enough info to reconcile the RPM shown in the HV control ECU's P0A0F freeze frame with the RPM shown in the ECM's P3191 freeze frame.