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Red Triangle and Codes P0A0F, P0121 (Still Operational)

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Billiam229, Jul 29, 2024.

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  1. Billiam229

    Billiam229 Junior Member

    Joined:
    Oct 9, 2022
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    Location:
    San Diego
    Vehicle:
    2009 Prius
    Model:
    II
    Hey There,
    I have a 2009 Prius with 246k and the original hybrid battery.
    I got a the Red Triangle of Death on a drive home earlier this month. The car made it home but there was a loss of power. Scanned it and got
    P0A0F [0x0A0F]
    Hybrid drive system - engine failed to start
    P0121 [0x0121]
    Throttle position (TP) switch A/accelerator pedal position (APP) switch A - range/performance problem
    Accelerator Pedal Position Sensor / Throttle Position Sensor A Range / Performance
    I cleared the codes and drove around the neighborhood. And it was operating normally. Eventually did reproduce the issue, same codes.
    In both cases it was a hot day and I had started the AC some time beforehand.
    Cleaned the MAF sensor but really didn't see any debris or dirt. The inverter pump is running too (I can see turbulence in the fluid container.)
    Since cleaning the MAF sensor, the car is running normally. I've put mileage on it driving around town. But I'm hesitant to do a longer trip especially in the heat.
    Any suggestions to get my confidence back in my ride?
    Thanks,
    Bill
    P.S. There is also a code P0420 related to my catalytic converter:
    Catalytic Converter System Bank 1 Efficiency Below Threshold
    But I've been told the cat needs to be replaced. It's intermittent.
     

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  2. Brian1954

    Brian1954 Senior Member

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    Vehicle:
    2011 Prius
    Model:
    III
    You have a problem with the throttle body or the wiring to the throttle body. Check the wiring first. If wiring checks out okay, them look at replacing the throttle body with a used one.
     
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  3. ChapmanF

    ChapmanF Senior Member

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    Vehicle:
    2010 Prius
    Model:
    IV
    The one-liner "fortune cookies" for those throttle and pedal sensor codes can be confusing, because the throttle sensor and pedal sensor are completely different items but their trouble codes all share the "throttle / pedal position sensor / switch" wording.

    Brian1954 has given the right call, P0121 (sensor "A") is about the throttle and not about the pedal.

    There's more about those sensors (and why the codes are the way they are) in this post.
     
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  4. ChapmanF

    ChapmanF Senior Member

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    Woops, can't edit any more, the post I meant to link was this one.
     
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  5. Billiam229

    Billiam229 Junior Member

    Joined:
    Oct 9, 2022
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    Location:
    San Diego
    Vehicle:
    2009 Prius
    Model:
    II
    Thanks Brian! I found some videos on cleaning/replacing the throttle body. And seemed like I could find a used one on car-part. But I'll check the wiring for anything loose that might be affected by the heat. Seems like good easy first step. I originally thought the P0A0F was causing the P0121 but sounds the other way around. Thanks also ChapmanF!