P0171 & P2195, Normal Driveability

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by BuckleSpring, Oct 9, 2023.

  1. BuckleSpring

    BuckleSpring Junior Member

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    Figured I'd post this in a separate thread w/ a more apt title. A few weeks ago, my Gen 2 was suffering from a P0A0F and a P3190. After cleaning the MAF, Throttle body, and PCV, the issue seems to be resolved.

    Car has been driving pretty well for the past couple of weeks. No more P3190 or ICE failing to start.

    However P0171 and P2195 still seem to return at random. MAF and throttle body have been very thoroughly cleaned, intake was cleaned, new air filter, cleaned the PCV valve, etc. If it's not the MAF, which i don't think it is considering I cleaned it and my P3190 hasn't returned, I'm not sure what else could be causing it. Vacuum line to the PCV looks fine, no obvious cracks in the intake boot, idle quality seems fine, which is where i think a vacuum leak would be most noticeable if that is what it is? I'll include some screenshots of the upstream O2 Sensor data.

    Voltage seems slightly higher than normal, but it's not constant, and it's not wildly out of spec like I'd think a dead sensor would be showing. I didn't remove the TB, so I think the gasket for that would still be fine, and like I said my idle quality seems fine. Any thoughts?
     

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  2. mr_guy_mann

    mr_guy_mann Senior Member

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    When the car sets those codes, look at what the freezeframe data shows.

    In particular: upstream A/F and downstream O2 sensor voltages, RPM, MAF, Short Term & Long Term Fuel Trims, MPH (vehicle speed).

    Also go for another drive, say above 40 with the ICE running (EV mode doesn't give much useful ICE data). Get the same data as above.

    Looking at your pics, A/F sensor seems active (3.2-3.3V), STFT moves as it should, but LTFT seems to stay near +14% at cruise and idle. Could be a number of things (vacuum leak is unlikely).

    Here's one way to check the MAF. Run your car under the same conditions as shown on this chart and note the MAF readings in grams per second. (known good data from my 2006 at around 500 ft elevation - you may have to adjust your readings if your are at much higher altitude)

    Screenshot_20220825-002058.jpeg

    Posted via the PriusChat mobile app.
     
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  3. BuckleSpring

    BuckleSpring Junior Member

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    I will go out for a drive this evening and try and get freeze frame data. MAF inconsistencies are a possibility I was considering.... The sensor on it doesn't seem to be OEM, I'm not sure what brand it is, but it's the one that came on the car when I got it ~40k miles ago.

    Yeah the LTFT was what was confusing me, upstream/STFT data seems to move correctly and respond to throttle input, but LTFT is weirdly high, usually between 13 and 15 when cruising at 45-60mph. I'll try and replicate the MAF conditions in the screenshot and write down the data, mine will probably be *slightly* off because I'm at ~1800ft altitude, but it should show if something is up.
     
  4. mr_guy_mann

    mr_guy_mann Senior Member

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    STFT is there to keep the A/F sensor on whatever target that the engineers want. Ideally it should stay near 0.

    If A/F moves away from the desired value, then STFT makes a correction, (+%) to make a positive correction {adds fuel to the base injection time}, while (-%) makes a negative correction {subtracts fuel from the base injection time}.

    If STFT moves away from 0 by more than a few percent , then LTFT makes a correction to bring it back to 0. There are different LTFT values for different combinations of RPM and load, and these are stored in ECM memory. Idle conditions are different from accel or highway cruise, etc. LTFT ideally should be near 0 +/- 5%.

    ST + LT = total FT (for example: +5%ST + +5%LT = +10%total, +2%ST + -7%LT = -5%total)

    You can make your MAF correction value. Take barometric reading at 500' (29.4"Hg) and divide by reading near 1800' (28"Hg). Then multiply the result by your MAF readings and see how close they are to mine.

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    #4 mr_guy_mann, Oct 12, 2023
    Last edited: Oct 12, 2023
  5. BuckleSpring

    BuckleSpring Junior Member

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    I was finally able to go out for a drive and get some data.
    • 0.09g/s engine off
    • 6.8-7.8g/s 1300rpm cold idle
    • 5.85-6.0g/s @2500rpm cold
    • 16.6g/s slowly dropping to 15g/s during initial force charge, RPM starting at ~2375 and ending at 2125
    • 5.45g/s WOT Hot
    • 4.15g/s at "hot" idle @ ~1250rpms (was unusually cold out today and wasn't able to get the car above 150F on my 15 minute drive into town
    • 5-4.6g/s @2500rpm WOT when hot and in Park
    • 7.43g/s @1300rpm idle when restarting the car after sitting for ~10 minutes (ran into the store to grab something)
    • 54.68g/s @5000rpm WOT hot

      And I'm attaching a screenshot of the freezeframe data
      Screenshot_20231015-214856.png
     
  6. mr_guy_mann

    mr_guy_mann Senior Member

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    If I look at that freezeframe, I would have to say "Liar-liar, pants fully on fire".

    Specifically, the A/F sensor is reporting about 4.0V, which is crazy lean. But it's less than fuel cut (5.0V). The A/F voltage would explain Fuel Trim of +55% and your code (+36% added to +19%).

    However, B1S2 O2 is reporting full rich (almost 1.0V).

    So, S1 and S2 are reporting opposite conditions. It MIGHT be possible that the FF snapshot happened exactly in the middle of a fuel cut for decel - EV mode transition, BUT something else would have had to cause FT to go erroneously high. If there was some other fault, then the S2 O2 should read at most around 700mV ("normal" if the system can keep fuel control) or near 0V is the engine is that lean.

    Short form, if your FT go that high at cruise and S2 reads near 1.0V, then the S1 A/F sensor is lying (biased) and should be replaced (Toyota or Denso from a reputable source - no counterfeits please).

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  7. BuckleSpring

    BuckleSpring Junior Member

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    I would personally ignore the downstream sensor data, It's probably not accurate whatsoever. The car has had a P0420 & P0037 & P0138 for a while, so that sensor is most likely just dead

    So you'd agree that S1 is definitely having some kind of issue? My MAF data isn't 100% identical to yours, but it also doesn't seem that off. I was debating on replacing it with an OEM one anyway to rule it out?
     
    #7 BuckleSpring, Oct 16, 2023
    Last edited: Oct 16, 2023
  8. BuckleSpring

    BuckleSpring Junior Member

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    As an update: I've been driving the car back and forth on my ~20ish mile "test loop" for the past couple of days, monitoring things. My MPG has dropped down to 29 so something is definitely up. Downstream O2 is sitting at a pretty consistent 0.02V when warmed up, so I'm just gonna go ahead and call that sensor dead.

    More worrying is the Upstream Wideband O2 voltage. On the drive home tonight, with the car fully warmed up, doing ~50mph w/ a slight uphill grade, sensor voltage was rather high (see attached screenshot)
    Screenshot_20231016-214531.png

    Car also has a very distinct fuel smell when exiting upon parking it. Current working theory is a dying upstream sensor reading lean that's forcing the ECU to increase injector pulse continuously since the upstream sensor is stuck lean?

    Car still seems to drive fine, minus the MPG loss. ICE starting is fine. I will probably grab a known-good used OEM MAF sensor this week since there's one locally off of a parts car for cheap to rule it out. Due to it running normally, I'm still thinking it's not a vacuum leak, especially with no MAF correlation codes or anything?
     
  9. mr_guy_mann

    mr_guy_mann Senior Member

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    If the ICE was actually running (not decel/EV mode, injector volume more than 0), there is no way the A/F could be 4.9V.

    Again, around 3.3V is normal operation and 5.0V is fuel cut. Running that lean SHOULD flag a low engine power or engine failed to start code.

    I agree, replace the A/F with OE-Denso and recheck operation.

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  10. BuckleSpring

    BuckleSpring Junior Member

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    Out getting more data while I await a new MAF and O2 sensor in the mail. The high upstream O2 voltage isn't a fluke. This screenshot is with the ICE at ~170F, Cruise set at 58MPH, ICE is definitely on as you can see by the RPM and commanded throttle input. Definite raw fuel smell behind vehicle after parking it

    When the car is cold and idling, O2S1 Voltage seems to be ~3.5, whenever it gets warmed up, it stays between 4.85 and 5v consistently while driving. When flooring it for an extended period, it stays at 5v. Car still seems to drive completely normally (maybe a little rougher than usual ICE engagement/disengagement. MPG seems to be in the 21-24 range, I've basically blown through a full tank in the past 125 miles

    Screenshot_20231019-193821.png
     
    #10 BuckleSpring, Oct 19, 2023
    Last edited: Oct 19, 2023
  11. BuckleSpring

    BuckleSpring Junior Member

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    I have an update:
    Finally got around to replacing the MAF, no change.
    Bought an upstream O2 sensor, installed it, and have been driving it back and forth to town over the past couple of days.
    Haven't gotten any OBD2 data yet, but my average MPG has jumped from mid-20s to about 47... so I think it's safe to say that was the issue.

    Very odd considering the upstream O2 was reading correctly in mixed throttle driving and fell to the correct value when the ICE was off. For anyone else reading with the same issue: My O2 sensor would slowly increase in voltage to 5V when cruising at a constant throttle amount (I tested it with the cruise set at 55 on a relatively flat road I go on frequently so I could replicate results).
     
  12. mr_guy_mann

    mr_guy_mann Senior Member

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    Good to hear the update.

    Hopefully anyone who finds this thread in the future will follow the data and test the system.

    Posted via the PriusChat mobile app.
     
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