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O2 Sensor/O2 sensor Heater Not Ready SOLVED!

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by DMil, Jan 5, 2023.

  1. DMil

    DMil New Member

    Joined:
    Dec 30, 2022
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    Location:
    Austin, Tx
    Vehicle:
    2009 Prius
    Model:
    II
    2009, 211K miles. No DTC, just showing Not Ready for O2 Sensor and O2 Sensor Heater on an OBDII scanner.

    No amount of driving or type of cycle made it turn Ready. This will prevent it from passing inspection for our county, so something I have no choice but to deal with.

    I put in a new Denso (OEM for Toyota) upstream O2 "A/F Ratio" sensor even though I had no error code. But I was down to 38mpg, and it's pretty old, so I know something wasn't happy, and this "Not Ready" is saying things are not OK there. It's fairly easy to get to and change (but there is drama about the tool needed, read below).

    O2 Sensor and O2 Sensor Heater went READY after about 15 min of driving. Cleared the codes to reset it, yep about 15 min of driving to get to READY again. Also jumped to 41mpg.

    This is weird that it doesn't report this as a bad O2 sensor.

    FYI the Prius O2 sensor is 22mm, but none of the regular sockets work on the upstream one because there's a metal heat shield cup around it. The ratchet-on-end type would fit into the cup technically, but the Prius bay has no clearance for that length and it's impossible to use.

    Instead you can get a "long" crowfoot type 22mm (or 7/8") O2 sensor socket, but you must grind its outer diameter from 33.5mm all the way down to 31.75mm. AND crowfoots come in two types, the short Tekton one could NOT reach the nut on bottom even after grinding. I found a longer one, pretty sure it was the Advance Auto "Performance Tool" crowfoot O2 sensor. THAT one has the length to reach the nut inside the cup. About 15 min of grinding with vice grips and a cup of cooling water got it down to 31.75mm and it worked great!
     
    #1 DMil, Jan 5, 2023
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  2. Tombukt2

    Tombukt2 Senior Member

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    Location:
    Durham NC
    Vehicle:
    2009 Prius
    Model:
    Base
    So you're not showing ready is not the car ready light You're talking about the mill steps on the top of your OBD scanner that tell you whether the O2 sensors are doing their job and changes from red yellow to green this is not in the car to be clear? It's not very easy to understand the way it's stated in the text so you're able to drive the car and the car goes to ready mode it's just your scanner is telling you that the O2 sensors are not heating and doing their job or whatever? My second question is because of this your car has no codes at all? I find that interesting I would think you would at least have the PO420 or something similar related to the given sensors 02 up or down whichever That's very interesting I drive the same model car you do I think another person posted about a '09 here from another country and it turns out it's actually a generation 3 which is 2010 and up in the US appears you're in Texas so I hope we're talking about a generation 2 1NZ.
     
    #2 Tombukt2, Jan 6, 2023
  3. ChapmanF

    ChapmanF Senior Member

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    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    I read the post as meaning that the O₂ sensor and O₂ sensor heater emission monitors were showing "not ready" status when queried with a scan tool. Not that the car wasn't going READY. That wouldn't make sense, as the post described driving it around.
     
    #3 ChapmanF, Jan 6, 2023
    Tombukt2 likes this.
  4. mr_guy_mann

    mr_guy_mann Senior Member

    Joined:
    Sep 3, 2020
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    Location:
    NJ-USA
    Vehicle:
    2006 Prius
    Model:
    Four
    What can sometimes happen, is that something is "partly bad". The ECM runs tests to check function of the engine control components. When something passes a test by lots, then "it's all good". If it fails by lots, it's bad (and sets a code). Either way the ECM completes the monitor.

    However, if something is marginal and just barely passes the test, then the ECM is often programmed to repeat the test "many" times before it determines if the parts/system passes or fails. A/F-O2 sensors are top of the list for things that can cause a monitor to "hang" & not complete.

    Posted via the PriusChat mobile app.
     
    #4 mr_guy_mann, Jan 7, 2023
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