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Another P0171 story

Discussion in 'Generation 1 Prius Discussion' started by dabard051, Aug 23, 2021.

  1. dabard051

    dabard051 Tinkerer-in-Charge

    Joined:
    May 19, 2009
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    Location:
    Rochester, NY USA
    Vehicle:
    2002 Prius
    Model:
    N/A
    The victim: 2002 Gen I Prius, 287k miles, half in FL, half in the Northeast. MPG about 39.

    Started getting intermittent CEL with DTC P0171. Cleaned MAF & throttle body no joy. Replaced MAF, cleaned throttle body again, no joy. In fact, frequency of DTC increased.

    So thinking to start looking for vacuum leaks (next on the fault list), I looked under the car, and it was noisier than I liked when running. But no apparent leak in exhaust system. So I decided to patch the exhaust leaks that I suspected were behind the shield that Toyota welds to the bend in the exhaust just past the cat converter and prior to the HCAC. Removed the shield (cut close to welds; about half an hour with a Dremel and a couple of cutting wheels), and revealed much corrosion and cracks in the pipe... hence the exhaust noise.

    Patched the holes and cracks with muffler putty and covered the pipe section with high temperature exhaust tape, and I'm surprised, right now the DTC is NOT coming back after 30 miles of driving.

    So a question
    if there is enough leakage just past the downstream O2 sensor, is that a possible cause for P0171?

    <edit> so, after a few more miles, the code is back... it just took longer than previously (sometimes it would occur in 6 miles). Did not need to be in a WOT (Wide-Open Throttle) condition to set the code.

    BUT: after patching the holes in the exhaust, the car is a LOT quieter when running on ICE...

    Question #2: if folks have fixed P0171 with a vacuum leak, where did they find the leak?
     
    #1 dabard051, Aug 23, 2021
    Last edited: Aug 23, 2021
  2. mroberds

    mroberds Member

    Joined:
    Nov 6, 2010
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    Location:
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    Vehicle:
    2001 Prius
    Model:
    N/A
    I don't think it caused a P0171, but I found a split in one of the PCV hoses that connects to the throttle body ('01 with 235k). If I remember correctly, it was the hose that connects towards the front (FRONT) of the car. The split was an inch or two above where it connects to the throttle body, just where the hose starts to turn away from vertical.
     
  3. Q*bertZ

    Q*bertZ Member

    Joined:
    Oct 22, 2019
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    Location:
    greenville south Carolina
    Vehicle:
    2002 Prius
    Model:
    N/A
    2002 Gen 1 Prius 305,000 miles. I had the P0171 error. It ended up being all my fuel injectors were clogged. The engine said it had my injectors wide open, and even though my miles per gallon said 39mpg I was still only putting in gas for about 48mpg. After changing the injectors the fuel trim went down and the mpg reflected 48mpg. My Prius now has 332,000 miles on it and is running great.
     
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