P0101 and P0127 codes showing

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Mendel Leisk, Dec 22, 2024 at 9:56 AM.

  1. Mendel Leisk

    Mendel Leisk Witness Leader

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    Got the check engine light yesterday, and Dr Prius showed:

    P0101 (MAF sensor issue)
    P0127 (overly rich air/fuel mix)

    I’ve tried spraying the sensor, dismissed the codes, and topped up the gas (about 12 liters).

    I’m suspecting bad gas, but not sure. Last fill up was a different station than usual, pump was incessantly shutting off (incidental I know). Maybe more telling: ever since that fill up, car seems pokey, and displayed liters per 100 kms stubbornly higher (worse).

    I did the code reset before driving to top up gas. Car revd unusually for first block or so (recalibrating?). I also noticed TPMS light was off (we’re currently on snow tires without sensors), so I’m not optimistic codes are gone.

    repair manual diagnostic flowchart is heavily Techstream involved (which I don’t have, currently). If symptoms/codes persist I’ll likely have dealership intervene. Not sure I want to dive into DIY acquisition of bootleg Techstream at this juncture, though I may reverse that.

    I really suspect that last gas station fill up, though not a certainty of course. Nothing else done of late, say that might cause a vacuum leak.
     
  2. Tombukt2

    Tombukt2 Senior Member

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  3. Mendel Leisk

    Mendel Leisk Witness Leader

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    See your response (embedded in quote):

    You should grab an AP200 before they disappear or whatever happens to em

    thanks, will look into that. I did read the honeymoon is over with it? Maybe still worthwhile though? Amazon.ca says $99.00 CDN. And it’s subscription, with one free car (all I need).

    not sure if it’s capable of walking through Techstream diagnostics?

    again, dealership intervention might be most prudent, considering all circumstances. I know…
     
    #3 Mendel Leisk, Dec 22, 2024 at 10:01 AM
    Last edited: Dec 22, 2024 at 10:11 AM
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  4. BiomedO1

    BiomedO1 Senior Member

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    According to those codes, you should've noticed a sizeable mpg decrease over the past few fill-ups. Check for leaks between the MAF sensor and your intake manifold gaskets. Any leaks along that pathway would/should throw those codes - unless you actually have a bad MAF. A bad MAF sensor would lead to either a lean or rich burn, depending on which way the MAF is failing. I would probably drop a new MAF into it before trying the dealership; If it's going to less than the diagnostic fee. The dealership jockeys would probably do the same to rule out that sensor failure. Most of those kids likes to use their brains to surf the web instead.:sleep:
    A quick way to check for leaks is to fire up the engine and use propane gas torch. Don't light the torch, just turn it on and run the gas over the suspected leak areas. Engine idle should increase, if there's a leak there. That's also a quick easy way to find vacuum leaks.;):whistle:
    A failing O2 sensor can also cause a rich mixture, but you'll need a better scan tool to diagnose that.

    Good Luck....
     
    #4 BiomedO1, Dec 22, 2024 at 10:28 AM
    Last edited: Dec 22, 2024 at 10:34 AM
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  5. Tombukt2

    Tombukt2 Senior Member

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    Yeah I keep a bunch of these kind of things marked in a drawer so I can do swaps like that to see because then some of this stuff it's hard to even tell in the freeze frame dating It's quicker to change the part than it is to sit there with the tablet in hand looking at rows and rows and rows of numbers and percentages I can stick an MAF on generally before the tablet boots or close to it
     
  6. Mendel Leisk

    Mendel Leisk Witness Leader

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    I'm skeptical about loading up the parts cannon just yet, through Amayama, even the generic equivalent would be around $110 CDN all-in. When I cleaned the one in there it looked pristine, fwiw. To, maybe a red herring, but it seems like this started on the heels of that sketchy gas fill up.

    Attached is the Techstream-laden diagnostic procedure from Toyota, for P0101 (plus P0102, which is referenced):

    As far as I know, the check-engine light came on with the car fully warmed up, on a steep uphill. Residential neighbourhood, doing about 50 km/h. At least that's the first I noticed it.

    Guess I'll wait-and-see for now. I don't think the MAF sensor cleaning was necessary or did anything, but I'm hoping the code clear plus the dilution of the possible bad gas may do something.
     

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    #6 Mendel Leisk, Dec 22, 2024 at 11:34 AM
    Last edited: Dec 22, 2024 at 11:48 AM
  7. Tombukt2

    Tombukt2 Senior Member

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    I've got a Mitsubishi lancer that's in here right now with a sketchy fill up at a known not good place to fill up and all of that and it's bogging down and running poorly and everything on the car looks pristine and well taken care of even though the car is 23 years old or so and it runs great until you floor it and of course this is a full gas car not a hybrid so no point here but so yeah bad fill ups are real thing
     
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  8. Mendel Leisk

    Mendel Leisk Witness Leader

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    Yeah I only managed to get in 12 additional liters (3+ US gallons); wish it was more.
     
  9. Brian1954

    Brian1954 Senior Member

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    Check the electrical connector to make sure it is fully engaged. Disconnect the connector, then use electrical contact cleaner. Let the connector dry and put it back together again.
     
  10. Mendel Leisk

    Mendel Leisk Witness Leader

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    Yeah did that, in the course of cleaning the sensor. Again, looked pristine.
     
  11. bisco

    bisco cookie crumbler

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    mendel, why does google show P0127 as 'intake air temp sensor'. is that part of the maf?
     
  12. Mendel Leisk

    Mendel Leisk Witness Leader

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    I'm seeing "running rich" and mention it might be MAF sensor related.
     
  13. ChapmanF

    ChapmanF Senior Member

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    Good catch—I just assumed Mendel had looked up the codes, didn't double-check.

    P0101 is an interesting code. The ECM computes two estimates of the load on the engine—one based on the MAF reading, one based on "driving conditions"—then sets the code if the estimates are not close enough to each other.

    [​IMG]

    P0127 is puzzling because the 2010 repair manual copy I'm looking in doesn't list it as a code the car can set. Being a P0 code, it has to mean the same thing in any car that can set it, so according to a list of the standard P0 codes, "Intake Air Temperature Too High" would be the ticket.

    [​IMG]

    The intake air temperature sensor does happen to be combined with the MAF sensor (it's the obvious blobby thing you see when you look at the MAF sensor, whereas the actual MAF sensing elements are tiny wires deeply buried inside it).
     

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  14. Mendel Leisk

    Mendel Leisk Witness Leader

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    Yeah I noticed, there's a single, relatively exposed "resistor" on one side, and two more, deeper down on the other side.
     
  15. PriusCamper

    PriusCamper Senior Member

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    Stay away from the Stealership because you're more educated on Prius than the dummy they'll put in charge of ripping you off...

    Does your car get parked in a garage? Or outside?

    Based on the insane rainy weather / flooding we've been having I bet you got water in all the wrong places and need a really long drive to sunnier places with lots of tanks of gas to dry everything out.

    In the meantime, reset your systems with a 12v disconnect and maybe order the cheapest MAF sensor you can find online as a back up plan.
     
  16. Mendel Leisk

    Mendel Leisk Witness Leader

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    It was a long, early morning drive, and yeah raining. I cleared the codes with dr Prius and with a test drive after that, ostensibly to top up gas, no warning lights (including TPMS which should be on), I could hear the engine doing some odd rev up, apparently recalibrating stuff.
     
    #16 Mendel Leisk, Dec 22, 2024 at 3:39 PM
    Last edited: Dec 22, 2024 at 3:44 PM