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Red triangle, limp mode, P2122, P2138, B2271, C1378

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by DMAndy, Jul 17, 2024 at 6:11 PM.

  1. DMAndy

    DMAndy Junior Member

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    I have had a recurring problem for at least a couple of months now.

    I am driving along merrily, the red triangle pops up randomly, the car goes into limp mode, electric motor working only, top speed of 10 mi/h. If I disconnect the aux battery for a few minutes, the car drives again, but not for very long. The longer I wait, the longer the car will drive before the same thing happens again.

    Thinking about it, this has only happened when I started the car after a few days in the garage, parked for a while, then went on my way again. I have driven 50 miles with no problems without parking. Today, I have driven less than 12 miles, but parked for 2 hours after 6 miles, and had to limp home for the last half mile.

    Does anybody have any ideas? I initially assumed the P2122 and the P2138 codes were because of the limp mode, but maybe not?
     
    #1 DMAndy, Jul 17, 2024 at 6:11 PM
  2. Tombukt2

    Tombukt2 Senior Member

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    Now this has something to do with your throttle position sensors gas pedal position sensor that sort of thing You need to look those up someone here can give you the work up for those usually it's corroded wires and things like that a plug that's been knocked loose etc there are a couple of sensors that can be involved here someone will post the manual workup probably from the factory at some point.
     
    #2 Tombukt2, Jul 17, 2024 at 6:59 PM
  3. DMAndy

    DMAndy Junior Member

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    Thanks. What makes me wonder is that I only get this error when I drive the car, park it and drive it again. Left for a few days and driven in one go, it is fine.
     
    #3 DMAndy, Jul 18, 2024 at 2:24 AM
  4. ChapmanF

    ChapmanF Senior Member

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    The car has both a throttle position sensor (on the throttle, out under the hood) and a pedal position sensor (on the go pedal, under your foot), and those two are two totally separate parts, connected to different ECUs, with different trouble codes.

    The P2122 and P2138 codes are both about the pedal position sensor, under your foot. More at this post.

    The car definitely goes into a limp mode when it mistrusts the input from the go pedal. The other way lie lawsuits.
     
    #4 ChapmanF, Jul 18, 2024 at 11:30 AM
  5. DMAndy

    DMAndy Junior Member

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    Thank you @ChapmanF . I sincerely hope you have been well since you single-handedly solved my last car related issue 4 years ago. (installed aux battery the wrong way around, took out fuses, put them back the mirrored way around)

    So in this case, my next step should be replacing the gas pedal, right? Also, any idea why the error has only come up after driving fine and parking for a while? (I can get to anywhere, I have trouble coming back.)
     
    #5 DMAndy, Jul 19, 2024 at 2:52 AM
  6. ChapmanF

    ChapmanF Senior Member

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    I would probably want to do some troubleshooting first. The codes from the ECU are complaining about the voltages reaching the ECU from the pedal sensor. The troubleshooting steps in the manual surely include simple checks on the wiring before concluding the sensor is bad. If you have a scan tool that can show live data, you can watch the VPA1 and VPA2 readings while moving the pedal, and maybe see what the complaint is really about. The post that I linked to above includes a graph of how the two signals are intended to relate to each other.

    (It's possible the ECU live data will show the two signals already translated from voltages to pedal %, in which case you wouldn't be looking for that graph relationship, but just for them to be close to equal.)

    If your scan tool can retrieve freeze frames for the P2122 and P2138 codes, you can see what the two readings were at the time the code was set, which ought to give a pretty clear idea what the complaint is about.

    None. Maybe it'll be interesting to find out.
     
    #6 ChapmanF, Jul 19, 2024 at 12:55 PM
  7. DMAndy

    DMAndy Junior Member

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    Having thought about it more, I think the error has only come up when the cabin became hot for a while in the sun. Even after that it will drive for a while, then I get the red triangle.

    I have an older version of Techstream, I'll check if I can get real time data on VPA1 and 2 readings. Do you know if it does freeze frames?
     
    #7 DMAndy, Jul 19, 2024 at 1:10 PM
  8. ChapmanF

    ChapmanF Senior Member

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    Techstream does all the things.
     
    #8 ChapmanF, Jul 19, 2024 at 1:19 PM
  9. DMAndy

    DMAndy Junior Member

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    Great, I'll go see what I can find out. Thank you.
     
    #9 DMAndy, Jul 19, 2024 at 1:34 PM
  10. DMAndy

    DMAndy Junior Member

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    I made a couple of videos, but couldn't upload them, Priuschat doesn't like the extensions.

    The two pedal position sensors seem to be 16.5-18 percentage points out of sync, but I am guessing it's designed that way. But then there were no errors now.
     

    Attached Files:

    #10 DMAndy, Jul 19, 2024 at 2:24 PM
  11. ChapmanF

    ChapmanF Senior Member

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    Huh, so they preserve the voltage offset between the two signals as a % offset after converting to %. I wouldn't have guessed that, but I guess I've never had reason to look at mine closely enough to know one way or the other.
     
    #11 ChapmanF, Jul 19, 2024 at 2:56 PM
  12. DMAndy

    DMAndy Junior Member

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    Apparently so.

    Went for a drive, left the car in the evening sun for an hour, but it didn't get hot enough, drove some more, all was good. I'll have to wait for a sunny day for the error again and keep the laptop in the car.
     
    #12 DMAndy, Jul 19, 2024 at 4:20 PM
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