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How to Replace O2 Sensor 03-09 Mazda 3

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  1. step : Removing the Downstream Oxygen (O2) Sensor (0:31)
    • Raise and support the vehicle
    • Unplug the O2 sensor electrical connector
    • Thread the sensor wire out past the exhaust and frame
    • Remove the sensor from the exhaust pipe with an O2 sensor socket and ratchet or a 22mm wrench
  2. step : Installing the O2 Sensor (2:07)
    • Apply anti-seize to the O2 sensor threads
    • Thread the sensor into the exhaust
    • Tighten the sensor with an O2 sensor socket and ratchet or a 22mm wrench
    • Thread the sensor wire into place
    • Plug in the sensor electrical connector
    • Hold the wire in place with wire ties

Hi. I'm Mike from 1AAuto. We've been selling auto parts for over 30 years!

Now you're going to raise the vehicle with a jack and jack stands, or a two-post lift if you have that.

We're going to unplug this secondary O2 sensor. It's the downstream. Let me see if I can get my hand up in there. Just push in on the tab, squeeze and pull. Wow. Someone's been in here before. They put a plastic tie here, so I'm going to cut that.

O2 sensors have special sockets for them, so they slide over. If you have a boxed end wrench, you can try it and see if you can break it free. It's usually a 22mm.

This exhaust has no O2 code, so we're not going to replace it, and by removing it, make sure there's hopefully no damage to it.

Before I install the O2 sensor, I put high-temp anti-seize on the threads, and most O2 sensor, new ones, will come with a packet of this in it for this reason. These will strip out or freeze in there. Very common. I'm not going to get it on the vent holes, just on the threads.

Now I can line it up, start it by hand, and it is a specialty O2 sensor socket, which is a 22mm, so you can use a 22mm box end on a wrench if you can make it past that, which you probably won't be able to do. That's unfortunate, but these sockets are readily available, and I do believe I've seen them in the tools on That's good. Nice and tight.

Now we can run the cable up to the connector. I'm going to run it up over the middle here. Now that we're in this way, I can line the connectors up and connect it until I hear it click. There we go. This car has had little wire ties, so I'm going to take another little small wire tie and attach this here to this bracket. I don't want this wire hanging down, and I don't want it to hit the exhaust, so I'll just get a plastic tie and run it around there. Ah, here we go. I’m just going to run her up there, run it through.

Thanks for watching. Visit us at for quality auto parts, fast and free shipping, and the best customer service in the industry.

Tools needed for replacement:

    General Tools

  • Jack Stands
  • Floor Jack

  • Materials, Fluids, and Supplies

  • Anti-Seize Grease

  • Ratchets & Related

  • Socket Extensions
  • Ratchet

  • Specialty Tools

  • O2 Sensor Socket

  • Wrenches - Metric

  • 22mm Wrench

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