HCHII Replace Primary Oxygen Sensor

Discussion in 'Honda Hybrids' started by all_about_the_glide, Aug 6, 2014.

  1. all_about_the_glide

    all_about_the_glide Well-Known Member

    Desperate Straights

    Check Engine Light Lit, CEL CODES: P1172 P2A00, pointing to a primary O2 sensor failure and resulting rich fuel/air mixture. In ideal summer conditions, I was having trouble breaking 60mpg on any trip and filled two tanks under 56 mpg :mad:.
    Fixed by replacing the primary O2 sensor for a total of $157. Now, no CEL light, current tank sitting at 63mpg :Banane26: --here's how.
    First, let me thank member Mendel Leisk for his detailed valve adjustment thread that clearly explains how to remove the cowl cover and cowl, allowing easy access to the sensor (it may be possible to do this job without removing the cowl, if you can get your hand on the sensor's connector and trust yourself to remove it by feel only).
    The sensor sits in the exhaust manifold facing the fire wall, you can see it plainly once you remove the plastic spark plug cover.


    Must PDF from Mendel's thread:


    This YouTube video is a great primer. Tip: you do not have to remove the O2 sensor receptacle from its stand, the first part of the video.



    Denso OEM O2 Sensor (ships with bronze anti-seize): $146.25

    WD-40 with straw

    Zip Ties (to replace worn plastic cowl cover fasteners)

    10 mm wrench and socket (disconnect the negative battery terminal and 5 of the 9 cowl bolts)
    Electrical Tape (place roll over the negative battery post)
    12mm socket (4 of the 9 cowl bolts)
    Socket Extensions – to reach sensor and bolts.
    3/8 Socket Drive (I needed a ¼ inch for my 10mm socket, as well)
    Powerbuilt 22mm O2 Sensor Socket: 8.33
    Radio Security Code


    1. Disconnect Negative Battery Terminal.
    2. Place Tape Roll Over Battery Post.
    3. Follow directions in the above PDF and remove plastic cowl cover. You can pivot the cover to the left and avoid disconnecting the washer fluid line.
    4. Remove cowl by removing all cowl bolts except the center bolt that inserts horizontally. It is possible to loosen this and then slide the cowl out, there is a notch in the cowl not a hole. Makes it easier to get back in, too.
    5. Spray base of O2 sensor with WD-40 or equivalent to loosen.
    6. Wait a few minutes.
    7. Break O2 sensor free with socket and ratchet (very little effort in my case).
    8. Unscrew sensor by hand.
    9. Follow electrical lead by had to the connector...note the retaining clip the middle of the lead is fastened to, you will have to re-clip the new sensor.
    10. The connector is located in a bank of three electrical leads and fasteners, it is the one in the middle.
    11. Remove the connector by depressing the plastic lever (clip) on top...see picture below. Again, you do not have to remove the male connector from the stand (the part that runs to the engine computer).
    12. Dab bronze anti-seize on the new sensor's threads.
    13. Hand tighten the new sensor.
    14. Firmly, but not with excessive force use socket to tighten sensor-- ½ turn??
    15. Snap connector into male receptacle and stand.
    16. Fasten the middle of lead to the clip in 9.
    17. Reinstall cowl.
    18. Take a breather, installing plastic cowl cover flush takes patience and a cool head.
    19. Replace plastic cowl cover.
    20. Reattach negative battery cable.
    21. Turn ignition to ACC...enter radio code.
    22. Start car...hopefully no CEL, huge MPG.


  2. Mendel Leisk

    Mendel Leisk 2010 Prius (CAN Touring) Staff Member

    Thanks for the acknowledgment. ;)

    Nice write-up, I've bookmarked it! I think I finally twigged onto what you mention in step 4, that the deeply recessed center cowl bolt could be just loosened, the second time we pulled that cowl out. My son has the car and the Maintenance Minder came up with spark plug replacement.

    Regarding the "broken cowl fasteners", I found some black nylon license plate bolts made a good replacement.

    Obviously a Canadian source, but for description:


    Here's a couple of links, taking snapshots from my shop manual.


    Last edited: Aug 6, 2014
  3. all_about_the_glide

    all_about_the_glide Well-Known Member


    I will pick up a pack of the nylon bolts, I will have to remove the cowl at least once in the not too distant future. I still have to do the valve adjustment and I want to install a block heater, maybe clean the ERG system. I was able to replace the spark plugs without removing the cowl (two small ratchet extensions placed one at a time on the back bank of plugs).

    I looked under the hood this AM before I left for work and I'm still thinking it is possible to replace the sensor without removing the cowl. I will take pictures and post soon.

  4. Mendel Leisk

    Mendel Leisk 2010 Prius (CAN Touring) Staff Member

    Toyota Prius has a similar (maddening) cowl. It's (as far as I know) impossible to get the spark plugs out without cowl removal. And really frustrating: you can get at them, but there's a metal tube running down into the spark plug wells. When you try to extract it it's "boink", hitting the underside of the cowl.

    If you have a half hour to spare, there's a YouTube video on the removal of cowl. It's an insane amount of disassembly needed, including wiper blades and motors, lol.

  5. all_about_the_glide

    all_about_the_glide Well-Known Member

    I'll cross that bridge when our V travels another 100k miles.
  6. all_about_the_glide

    all_about_the_glide Well-Known Member

    I just looked at the engine...if you remove the air filter cover you might be able to get at the sensor's connector. If I had to do it again, I'd try to un-fasten the connector first, then remove the sensor from the exhaust manifold without removing the cowl. But the second it looked iffy the cowl's coming off.

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