2005 SWAP UPSTREAM O2 SENSOR- Rid Code P0420 Catalyst System Efficiency Below Threshold (Bank 1)

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Prius_Angie, May 3, 2018.

  1. Prius_Angie

    Prius_Angie Member

    Joined:
    Aug 9, 2015
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    Location:
    Kansas City
    Vehicle:
    2005 Prius
    Model:
    I
    Recently I received a DTC code P0420 prompting me from my CEL. The live feed data from my OB2 code reader revealed a consistent “0” on upstream O2 sensor, while downstream was noting 3-5.0 over minor throttle while I was parked in my garage. I assessed it as a BAD UPSTREAM O2 sensor. Also, helpful towards my deduction was that I just replaced the catalytic converter to my 2005 Prius a few months back. I scored a $4 used piece from a scrapped Prius at my local junkyard and went to work.
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    1. JACK UP CAR.
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    2. DESIGN, UPSTREAM O2 SENSOR. You will notice immediately that the sensor has a unique cap to it that adds to shield and help cool the O2 sensor. I decided to cut at it with a dremmel tool, vice order a special removal tool.
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    3. FROM BELOW, REMOVE UPSTREAM O2 SENSOR. Removed 2x screws to a small heat shield, providing me access to dremmel-cut away at the O2 sensor.
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    4. RE-ATTEMPT ACCESS, FROM ABOVE. I didn’t have enough O2 sensor access, so I had to try again and come from above. I dropped the vehicle off the jacks and tried from above. I removed the above heat shield and cut at the O2 sensor from above. That worked nice.
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    5. 22MM CRECENT OVER O2 SENSOR SOCKETS. For breaking the O2 seal, my purchased specialized O2 sensor sockets were less helpful than a HUGE 22mm crescent wrench. This was a frustrating venture that required an overall ~ 6 hours of frustration to include an overnight cool down for reflection.
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    6. ALUMINUM NOT COPPER ANTI-SEIZE. I couldn't find any copper anti-seize from any local auto part shops, so I went with what I had: Permatex Aluminum Anti-Seize. The initial testing at idle in my garage, produced a heavy amount of smoking and burning that quickly went away with time. Copper based formulas are limited to 1,800 degrees F and aluminum based formulas to 1,600 degrees F.
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    7. ROAD TEST. I cleared the CEL & DTC code via Techstream computer. After a road test of 200 miles later, i still have no problematic issues & CEL didn't reappear. I also had the OB2 reader running live feeds reflected during the road test drive: upstream “0.1-0.7”; downstream “1.0-3.5”.
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    #1 Prius_Angie, May 3, 2018
    Last edited: May 3, 2018
    bisco and SFO like this.
  2. Prius_Angie

    Prius_Angie Member

    Joined:
    Aug 9, 2015
    127
    85
    0
    Location:
    Kansas City
    Vehicle:
    2005 Prius
    Model:
    I
    UPDATE... prior to CEL light to this problem arising, my MPG dipped down to ~34MPG. Now after upstream O2 sensor swapout: 44 MPG.
     
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