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How To: 98 EX secondary O2 sensor replacement

Discussion in 'Engine Tech / Drivetrain DIY How-To's' started by J-Sap, Jan 8, 2010.



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  1. J-Sap

    J-Sap New Member 5+ Year Member

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    I have a 98" Civic EX and I have the error code P0138 coming up. I am fairly certain that the oxygen sensor is gone (it has almost 82,000 miles on the original sensor). I did not change anything else on the car and have not for several months when this came on. I purchased a replacement oxygen sensor for it that will bolt right on.

    I put the car on ramps and looked under the car and see that the second O2 sensor is on top of the exhaust behind the cat with very little space to get it off. I can not get my normal oxygen sensor drive socket on because there is no room and also have trouble getting a flare nut wrench on it because of the position.

    My question is how do you get this sensor off the car and how have other people done it???

    It looks like I could undo the cat from the exhaust on one side to give me more room or fully take it off but it is rusted a good amount and would rather not risk have to replace all of those parts.

    Any help would be greatly appreciated.
     
  2. RonJ

    RonJ Banned

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    If you clear the ECU, does the code return?

    It may be easier to just remove the cat to replace the sensor.
     
  3. J-Sap

    J-Sap New Member 5+ Year Member

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    Yes I can clear the ECU and the code comes back after a couple minutes.
     
  4. RonJ

    RonJ Banned

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    The O2 sensor is probably the problem, but be aware that there is some possibility that the cause could be a bad wire or less commonly a bad ECU.


    [​IMG]
     
  5. J-Sap

    J-Sap New Member 5+ Year Member

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    Thank you for the help RonJ.

    I ordered a crow foot socket that I should be able to get over the O2 sensor and get it off. I will post pics and update how it goes.
     
  6. J-Sap

    J-Sap New Member 5+ Year Member

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    Alright so I got my O2 sensor replaced. I can honestly say that on all the cars I have worked this Honda Civic was by far the hardest vehicle to perform a basic maintenance task on. I also documented it with pictures and figured I would do a quick write up.

    1. I drove the front of the car up onto ramps, put two jack stands under the car for safety, and blocked one of the back tires.
    2. Disconnect the battery. This is for safety and to reset the ECU.
    3. The O2 sensor is located under the car directly underneath the center console. It is easiest to get at from the passenger side.
    [​IMG]
    [​IMG]
    4. Depending on how much rust there on the sensor determines how much effort is needed to get the O2 sensor off. The safest and easiest way to get the O2 sensor off is to run the car for a minute or two in order to heat the catalytic converter up. This causes the metal to expand and should make it easier to pull the O2 sensor off. I was not lucky enough for this to work, I then tried a spray to loosen the bolt (failed as well). The final resort and what worked for me was an acetylene torch. Caution that this could damage the catalytic converter because it so close to the O2 sensor but if used fast and only on the area that needs it you will be fine. I also needed a special O2 sensor removal tool because of the clearance underneath the car I could not get a traditional O2 socket wrench on the old sensor or install the new sensor with it. It is a crows foot socket wrench that I ordered on amazon. It worked great for removal and installation.
    [​IMG]
    [​IMG]
    5. Once the sensor is out of the socket you will need to un-clip it in the car, the clip is located in the center console. In order to get to it you will need to remove the black box at the bottom. This is done with a screwdriver and one screw on the passenger side and driver side. Once the screws are out the plastic clip in that the screw went into will need to be removed (they just pop out) and then use a flat headed screwdriver to separate the two halfs of it apart.
    [​IMG]
    [​IMG]
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    6. Once it is apart the O2 sensor plug is located on the passenger side underneath the rug (I had to cut the rug a little to get at it). This comes undone by hand.
    [​IMG]
    [​IMG]
    7. There is a plastic washer that goes into around the O2 sensor wire that also needs to be pulled out and replaced. I recommend just getting a new washer from a hardware store because I was unable to slip the stock one around either side of the O2 sensor.
    [​IMG]
    8. Now install the new O2 sensor into the cat and run the wire through the hole in the firewall into the clip to connect it to the car. Don't forget to use some type of never seize on the O2 sensor threads so it can be removed again. A light layer on the threads is all you will need and don't get any on the sensor or it may be damaged.
    [​IMG]
    9. Installation of everything is the reverse of taking it apart, once it is all set hook the battery back up and put the car on the ground. You should have a new O2 sensor fully functional in the car.

    I put around 20 miles on the car today after doing this and have had no ECU or check engine light come up. Also my temp gauge is slightly lower then what is used to be, so I am hoping that I will get better gas mileage in the future.
     
  7. Esotericimage

    Esotericimage Taking an H-T break Registered VIP 5+ Year Member

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    nice write up..
     
  8. J-Sap

    J-Sap New Member 5+ Year Member

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    Quick update. The car runs great and went for a 400 mile commute earlier in the week. The gas milage inceased from 30 mpg to 36mpg, a very nice 20% improvement. Also the engine temp was noticably cooler and lower the entire drive.
     
  9. ej4sedan

    ej4sedan New Member

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    thanks for the write up.
     
  10. cpgoose

    cpgoose New Member

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    Hey guys...I just found this thread while I was searching around for help on replacing my O2 sensor. I'm trying to replace the same one as in this thread (the one by the cat), but I'm having a terrible time removing it due to rust on the sensor and on the cat. I even brought the car to Sears to have 2 tires replaced and asked them to do the sensor while they were there. When I came back to get the car they said they couldn't remove it and didn't want to hurt anything else, so they left it there.

    Hey J-Sap, were you able to get pictures of what you did like you mentioned?
     
  11. Jersey8

    Jersey8 B20: Detroit Muscle! Registered VIP Registered OG 5+ Year Member

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    try pb blaster, maybe a torch, maybe a 7/8" open end wrench instead of a socket (moar torque!)?

    you may need to remove the exhaust in order to get a betting footing...
     


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