air/fuel ratio sensor connector location?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by wddanie, Jun 17, 2012.

  1. wddanie

    wddanie Junior Member

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    I am getting code p0420 and want to replace the air/fuel ratio sensor and cannot figure out who to reach and remove the connector to the sensor. Can somone tell me how to do it? I read several threads about it and saw instructions for the rear O2 sensor but not the fwd air/fuel ratio sensor.

    I hope to remove it from below and avoid removing the inverter. From under the car I can see the cable leaving the sensor and I think I see it terminating in a connector on the left side of the engine. I can barely snake my arm up there and touch it, but I cannot get a good enough grip to press a release button and pull it free. I figure there must be an easier way so I decided to ask for help before proceeding.

    I got the rear O2 sensor changed in about 45 minutes.

    Thanks in advance for your help.

    Doug
     
  2. James Macnab

    James Macnab Junior Member

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    Hi Doug;

    Did you ever get a reply on this post? I realize this is an old post but I have an identical problem and cannot find out how to access the plug.
    I can't believe you have to remove the inverter or other engine components just to test this sensor.

    Jim Macnab
    Franklin, NH
     
  3. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Whether you believe it or not, the Toyota repair manual suggests that you remove the inverter (which requires removing the metal cowl tray that the windshield wiper motor sits in) for access to the A/F ratio sensor.
     
  4. James Macnab

    James Macnab Junior Member

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    Hi Patrick;
    Did you replace your primary AFR sensor. I have the Bentley Manual which has good detailed instructions.
    I can check resistance after I access the plug but then have to reconnect the electrics to check voltage and current etc.

    If you did replace the sensor, about how long did it take and were there any "gotchas" I should be aware off.
    I would also appreciate any feedback from ANYONE who has done this pair.

    Thanks
    Jim Macnab
    Franklin, NH
     
  5. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Hi Jim,

    No, I have not needed to do that yet. 152K miles on the 2004.
     
  6. johnjohnchu

    johnjohnchu Member

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    Just replaced both sensors last week.

    O2 sensor itself can be accessed from the bottom of the car. The electrical connection is inside the car under the carpet side wall (center section, passenger side). Took 30 minutes.

    The air fuel ratio sensor can be accessed from the engine compartment after removing only the windshield wiper mechanism. There is absolutely no need to remove inverter, or disconnect anything else, except the one electric connection associated with the wiper. Toyota repair manual instruction is way over kill unless you have a real big hand. The enclosed photo may give a wrong impression that the space around the electrical connection location is very small, but actually there is plenty of room. Took 30 minutes.
     

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  7. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Nice work and great photos! I assume that you also removed the sheet metal tray that the wiper motor is mounted to.
     
  8. Robo

    Robo Junior Member

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    I have a code 0420 and will try to replace air fuel ratio sensor. Is the electrical connection inside the car a snap connection, or do wires have to be spliced? Also, does the connection in the engine side thread through to the passenger side under the carpet?
     
  9. johnjohnchu

    johnjohnchu Member

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    The air fuel ratio sensor comes with a snap connector. No splicing is necessary. The electric connection itself is under the hood below the inverter. It is not necessary to remove the inverter to access the electric connection. Did not have a chance to trace the electric connection beyond the connector itself.
     
  10. leemcgee

    leemcgee Junior Member

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    Good morning, I have been debugging DTC codes 2237/2238 and what sounds like detonation in a failed catalytic converter in my old 2007 Prius (375,000 miles!), I just removed the wipers and cowl yesterday to look at the air/fuel ratio sensor connection, and my connector appears to be melted somewhat, that something maybe has gone wrong inside of it, it does not look good like the one in the picture above. Can the four wires each side be removed so I can get the connector out to look at it carefully? Can the four wires be simply spliced together to get the air/fuel sensor working again, will any cheap four wire connector work? Am hoping that there might be some help here before I do something stupid! Thanks, Lee
     
  11. valde3

    valde3 Senior Member

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    You can splice the wires together and remove the connector or use some other connector. But don’t solder the wires! Sensor takes very small amount of oxygen from those wires to compare exhaust gas to. And soldering would stop air entering the wires.

    But really you should figure things out before just putting a new sensor in. Or even repairing the connection. If old sensor is somehow shorted repairing the connection can just cause troubles. Just removing the sensor and possible short circuits should get the engine running pretty normally. If engine is running very badly just installing new sensor won’t fix it.
     
  12. leemcgee

    leemcgee Junior Member

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  13. leemcgee

    leemcgee Junior Member

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    Thank you Valde3! Your reply actually brings up some more questions for me.

    Any way I can test with multimeter whether the air flow sensor itself is shorted?

    The four wires going IN to the connector are a different color from the four wires going OUT to the air sensor. I do not know which wires to splice to which, if I was to take that route and found that the air sensor itself was not the cause of the short.

    Don't worry, I do not plan to touch ANYTHING until I feel that I have very sound and workable advice from this group. You guys are the best. -Lee
     
  14. johnjohnchu

    johnjohnchu Member

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    [QUOTE

    Any way I can test with multimeter whether the air flow sensor itself is shorted?

    [/QUOTE
    ]

    All images were extracted from Toyota Prius Tech Manual.
     

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    #14 johnjohnchu, Aug 2, 2016
    Last edited: Aug 2, 2016
  15. leemcgee

    leemcgee Junior Member

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    [/QUOTE]
     
  16. leemcgee

    leemcgee Junior Member

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    Thank you johnjohn a very clear and good picture, I will test this within the next hour here. Where did you get that .jpg picture from?

    Thanks again, -Lee
     
  17. johnjohnchu

    johnjohnchu Member

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    []
     
    #17 johnjohnchu, Aug 2, 2016
    Last edited: Aug 2, 2016
  18. johnjohnchu

    johnjohnchu Member

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    #18 johnjohnchu, Aug 2, 2016
    Last edited: Aug 2, 2016
  19. ChapmanF

    ChapmanF Senior Member

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    The first .jpg was a sample of what you see in the repair manual, and the second illustrates what you see in the electrical wiring diagram. Both (and a lot more) are available on techinfo.toyota.com.

    The wiring diagram, in particular, contains lots of information related to the questions you were asking earlier. For example, notice that the air-flow sensor has the label 'A5' next to it. In other sections of the wiring manual, you can find the part number for an A5 connector shell (in case you'd like a new unmelted one); another section shows you the physical wire harness routing and A5's location (in case you didn't already know) and so on.

    The repair manual is where you find the step by step instructions for what and how to test, starting with the DTCs you reported, in order to pin down what's really wrong.

    -Chap
     
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