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O2 code after stolen cat conv replacement has mechanic stumped

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by andrewe2, Dec 18, 2020.

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  1. andrewe2

    andrewe2 Junior Member

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    I joined the growing club of victims the other day. Fortunately my insurance covered most of the cost. My garage said thieves damaged the O2 sensor while stealing the catalytic converter and it had to be replaced. I picked up the car drove it about 4 miles and the check engine light came on with code P0136 (O2 sensor). Next day garage replaced the O2 sensor they had installed the day before (which checked out good). Picked the car up today and everything looked good for about 15 minutes on the highway and the light fired again (P0136). The car runs fine. I'm beginning to suspect that my garage may be out of their league on this one. It goes back to them in a couple of days but I'm concerned they're going to start shot-gunning the problem, replacing other parts. Any suggestions on what I should do or ideas on how to troubleshoot and fix the cause?

    Thanks

    Andrew
    2004 Prius with 215k miles
     
    #1 andrewe2, Dec 18, 2020
  2. Elektroingenieur

    Elektroingenieur Senior Member

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    • The oxygen sensor might be counterfeit or the wrong part. The Toyota part number is 89465-47070, and it would be best to buy one from a Toyota dealer, not from an online seller whose inventory may have been commingled with similar parts from less reliable sources. I expect the Denso equivalent (234-4623) would be OK, too, if bought from a reliable source.
    • See the troubleshooting procedure for P0136, P0137, and P0138 in the Repair Manual (more info).
     
    #2 Elektroingenieur, Dec 18, 2020
  3. dbstoo

    dbstoo Senior Member

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    Had a similar problem with Mom's Cadillac. A mechanic unplugged the sensor in order to get to a rear spark plug. Shortly after picking it up the CEL came on. She took it back and they pulled the code. Bad O2 sensor. They fed her a line of bull about having to drive it for an hour to reset the computer.

    I took a look. The shop manual gave instructions for checking the sensor with a volt/ohm meter. As I poked around to check the voltages I found that one of the connector blades was bent over and smashed, not making contact. I straightened it out with a pair of needlenose pliers and was able to get it back together. It worked again and the CEL cleared.

    I suggest that you check both the plug AND the socket.

    Dan
     
    #3 dbstoo, Dec 18, 2020
  4. andrewe2

    andrewe2 Junior Member

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    Interesting service bulletin specific to my year and problem. Thanks for pointing that out. I'll keep you posted.
     
    #4 andrewe2, Dec 18, 2020
  5. andrewe2

    andrewe2 Junior Member

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    I'm sorry to expose my ignorance but the bulletin says it applies to "2004 model year Prius vehicles produced BEFORE the Production Change Effective VIN shown below" JTDKB2#U#40028134 and my VIN is JTDKB20U440038208. Does it mean my Prius was produced after they fixed it?
     
    #5 andrewe2, Dec 18, 2020
  6. Elektroingenieur

    Elektroingenieur Senior Member

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    Yes, that’s correct.
     
    #6 Elektroingenieur, Dec 18, 2020
  7. mr_guy_mann

    mr_guy_mann Senior Member

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    Don't know what to say. It's a basic 4 wire oxygen sensor. 2 wires for the heater, 2 for the sensor signal. The connector is actually inside the passenger area so any damage would have been to the sensor pigtail/wiring. About the only bad thing that could happen is the heater wires shorting together and damaging the ecu.

    For diagnostics, once the sensor reaches operating temperature (that's why it has a heater) it puts out a voltage signal that varies with the amount of oxygen present in the exhaust gases. When there is lots of oxygen (aka "lean") it is near 0V, with very little oxygen it is near 1V ("rich"). The actual voltage at the sensor connector should match what the ecu displays on a scantool. That reading should change as you drive the car.

    One thing to watch for is if there is an exhaust leak that can allow outside air to be sucked in- that can skew the sensor reading.

    Posted via the PriusChat mobile app.
     
    #7 mr_guy_mann, Dec 19, 2020
  8. SFO

    SFO Senior Member

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    #8 SFO, Dec 19, 2020
    Raytheeagle likes this.
  9. andrewe2

    andrewe2 Junior Member

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    That's too bad, however, I erased the code and took it out for a "strenuous" 30 mile ride and no light, which would lead me to suspect there is some connection with the notion of an O2 sensor being effected by a new converter/exhaust as it "breaks-in" as described in the bulletin (only for my year) you pointed out, for which I'm impressed and grateful. I guess I'll just have to wait and see if the error occurs. Thanks again.
     
    #9 andrewe2, Dec 20, 2020
    SFO likes this.
  10. andrewe2

    andrewe2 Junior Member

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    Here's an update; looks like it was cat converter breaking in. CEL for sensor hasn't been on since.
     
    #10 andrewe2, Jan 10, 2021
    Jeff606 and SFO like this.
  11. andrewe2

    andrewe2 Junior Member

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    You were right on the catalytic converter break in. I wonder if you might have some insight into another mystery. My CEL has been coming up with a misfire on cylinder one (PO301) for almost three years. The garage replaced the plugs and some other component related to the injectors but not the injectors. It seems to come on more frequently in cold rainy (Bay Area) weather and possibly when I'm parked on a hill (nose down). Any thoughts? Does it sound like an injector?
     
    #11 andrewe2, Jan 10, 2021
  12. Elektroingenieur

    Elektroingenieur Senior Member

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    It could be the water leakage problem described in Toyota service bulletin EG063-05, “M.I.L. ‘ON’ DTC P0300, P0301, P0302, P0303, OR P0304,” December 16, 2005, discussed in this previous thread and several others.

    If not, there is a comprehensive diagnostic procedure for P0301 in the Repair Manual (more info).
     
    #12 Elektroingenieur, Jan 10, 2021
    SFO likes this.
  13. andrewe2

    andrewe2 Junior Member

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    Once again you may have solved my problem. Water leakage is a likely culprit due to fact that it happens more frequently in rainy weather and when the car is pointed downhill. I don't understand why independent garages don't seem to be aware of these TSBs. I'll keep you posted. Thanks again.
     
    #13 andrewe2, Jan 11, 2021
    Jeff606 and SFO like this.
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