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O2 sensor monitor never completes

Discussion in 'Gen 2 Prius Technical Discussion' started by david95376, Oct 30, 2019.

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  1. david95376

    david95376 New Member

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    Hello all. This is my first time posting on this forum. I have a 2008 Prius that I bought used in spring of 2018. For about 18 months on and off, I have driven the car in attempt for get all of the monitors ready. I have also followed the drive cycle specification.

    Within the past year, I have driven the car hundreds of miles with the following results repeatedly:
    - I reset the ECM
    - I drive hundreds of miles, frequently checking monitor statuses and DTCs
    - No DTCs ever appear
    - The only monitor left to complete is the oxygen sensor one
    - When I reach a certain mileage, the large red triangle appears, along with multiple amber lights, of which I forgot to take note
    - I reset the ECM again

    Does anyone know why the oxygen sensor monitor never completes?
     
    #1 david95376, Oct 30, 2019
  2. SFO

    SFO Senior Member

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    Welcome to PriusChat!

    How many miles are on the vehicle ?

    How are you monitoring for DTCs (which device, etc) ?

    When was the last time the oxygen sensor was replaced (upstream or downstream) ?
     
    #2 SFO, Oct 30, 2019
    Leadfoot J. McCoalroller and Raytheeagle like this.
  3. Aegean

    Aegean Active Member

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    Well I had another vehicle with the same issue. The monitors were never complete and therefore in Virginia I could not pass emissions to renew my registration. After extensive research and two dealer diagnosis visits it was never resolved. Luckily, I learned about a technicality, the Ford Excursion was over 8500 pounds and was allowed to pass emission with the old tail pipe sniffer.

    I am glad I do not have to deal with anything similar anymore because both my 2006 Prius are exempt from Emission testing in Virginia.
     
    #3 Aegean, Oct 30, 2019
  4. david95376

    david95376 New Member

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    The vehicle currently has a mileage of 166,520. I use an ELM327 WiFi OBD scanner along with OBD Auto Doctor on my laptop. The downstream O2 sensor was replaced earlier this year, with a Kwiksen brand OEM-compliant sensor. After a few months, the upstream O2 sensor was replaced with a new eBay one, which caused DTC P2237 to appear, so it was again replaced a few days ago with a used (junkyard-sourced) O2 sensor which had no DTCs. However, the upstream usually has a reading between 2 and 6 volts, according to a graph shown by OBD Auto Doctor, regardless of how many times I've replaced it.
    Screenshot from 2019-09-13 19-15-44.png
     
    #4 david95376, Oct 30, 2019
  5. david95376

    david95376 New Member

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    The above screenshot was when I had a family member drive the car with stop and go traffic.
     
    #5 david95376, Oct 30, 2019
  6. valde3

    valde3 Senior Member

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    After the fault lights come on did you read the codes? There has to be codes.
     
    #6 valde3, Nov 1, 2019
  7. SFO

    SFO Senior Member

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    Never heard of the application before, my guess is OBD Auto Doctor isn't offering you the DTCs needed.

    Please find a generally recognized app or program from this forum and try scanning again : Prius OBDII Third-Party Apps | PriusChat
     
    #7 SFO, Nov 1, 2019
  8. david95376

    david95376 New Member

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    Will try a different OBDII app, but the vehicle finally threw a code, P0A80. I might consider selling it at this point.
     
    #8 david95376, Nov 1, 2019
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