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random convo starter - what's the most frequent cause of the p0171/2 codes?

Discussion in 'Generation 1 Prius Discussion' started by ronlewis, Sep 13, 2024 at 8:05 PM.

  1. ronlewis

    ronlewis Active Member

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    It can be so many things. The service manual doesn't suggest any one over the others, and I can go through all of them one at a time, but maybe everyone's experience here (all three of you) will suggest one to start with. WTH?

    Mine drives fine on the highway. Noticed a slight shudder at idle and found the pending 0171 code.
     
    #1 ronlewis, Sep 13, 2024 at 8:05 PM
  2. ChapmanF

    ChapmanF Senior Member

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    Trick question? P0171 and P0172 are opposite problems.
     
    #2 ChapmanF, Sep 13, 2024 at 8:28 PM
  3. ronlewis

    ronlewis Active Member

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    I understand, but maybe the opposite of someone's frequent cause of a 71 is the cause of a 72. IDK. It's just a random survey. I don't think fuel pumps are a common problem, for example, but maybe everyone tells me they are and I start with the pita fuel pressure test versus, say, cleaning the throttle body. IDK.
     
    #3 ronlewis, Sep 13, 2024 at 9:04 PM
  4. ChapmanF

    ChapmanF Senior Member

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    I'm not sure I could think of how a dirty throttle body would be implicated in either one. Only thing more tedious than checking lots of things listed as trouble areas might be also checking things that aren't. :)

    You write that the manual "doesn't suggest any one over the others" ... but it does give a troubleshooting procedure with steps numbered 1 through 11. How Toyota picks the order of their troubleshooting steps may be kind of mysterious, but probably reflects some balance of what they've found the most common causes to be, with which checks are more or less of a pita.
     
    #4 ChapmanF, Sep 13, 2024 at 9:31 PM
  5. ronlewis

    ronlewis Active Member

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    All true, and understood. Let me see what the FB groups say.
     
    #5 ronlewis, Sep 13, 2024 at 9:59 PM
  6. TMR-JWAP

    TMR-JWAP Senior Member

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    I would say on a Gen 1 and Gen 2, a dirty MAF sensor is a common cause. I've been fortunate enough that both times I've had a P0171 (2 different Gen 2s) each has been resolved by cleaning the MAF sensor.
     
    #6 TMR-JWAP, Sep 14, 2024 at 11:04 AM
  7. Trombone

    Trombone Member

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    This. See also Patrick Wong's relevant post here: MAF Sensor, What is it, Where is it | PriusChat
     
    #7 Trombone, Sep 14, 2024 at 2:21 PM
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