Oxygen Sensor issues

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by d_w, Mar 7, 2025 at 11:20 AM.

  1. d_w

    d_w New Member

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    Hey all,

    My 2007 is throwing a p2195 code and occasionally a p0138. MPGs have dropped to low 30s. There is something up with the O2 sensors, so I am trying to narrow down the issue.

    I recently did a piston soak to help with an oil burning issue. Replaced the PCV, spark plugs, and valve cover gasket. Cleaned the MAG sensor. It all went well, I don’t *think* these codes are related.

    I’ve attached a log of a short city drive between 30-40mph. The A/F sensor data seems erratic to me, as well as the short term fuel trim.

    I have a replacement A/F sensor on order, but was looking for more opinions before changing out the part. Is there anything else it could be? Am I missing something? Any help is greatly appreciated.
     

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    #1 d_w, Mar 7, 2025 at 11:20 AM
  2. d_w

    d_w New Member

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    Here is another short trip log, mostly at highway speeds
     

    Attached Files:

    #2 d_w, Mar 7, 2025 at 2:18 PM
  3. dolj

    dolj Senior Member

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    Did you mean MAF sensor? Did you clean both the temperature sensor (at the side of the 'finger') and the airflow sensor (embedded inside the 'finger')?

    Did you disconnect the 12 V battery for a minute or two after you did all the work? You need to do this so it resets the EMC to defaults. Especially import after cleaning the MAF/throttle body.
     
    #3 dolj, Mar 7, 2025 at 10:47 PM
  4. d_w

    d_w New Member

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    Yes, the MAF. Typo. Everything on it got a good clean. I did disconnect the battery to reset the ECM but didn’t see any differences before and after.
     
    #4 d_w, Mar 8, 2025 at 10:08 AM
  5. dolj

    dolj Senior Member

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    After a reset, it takes several drive cycles for the ECM to relearn the optimum values. Anything from 5 minutes to 5 days.
     
    #5 dolj, Mar 8, 2025 at 8:52 PM
  6. mr_guy_mann

    mr_guy_mann Senior Member

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    Do you have freezeframe data for either code? It's a bit odd because P2195 is for the B1S1 Air-Fuel ratio sensor stuck lean. That should show in data as at or near 5.0V. Short Term Fuel Trim should go positive to compensate.

    Your graphs show (unexplained) dips in A-F voltage down to 1.4V, that's indicating (or at least reporting) a rich condition, and STFT is going highly negative in response.

    Here's the bits in the MAF that need careful attention. clean_maf.JPG

    Posted via the PriusChat mobile app.
     
    #6 mr_guy_mann, Mar 9, 2025 at 4:01 PM
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